chapter three fuel system
Contents
1. If you have this type of system put it on the diagnostic check list in addition to the gauge fuel transmitters and connections The work related portion starts with removing the wing access cover for the suspect transmitter Obviously you need to heed all safety precautions when working in this area If necessary drain sufficient fuel from the tank to avoid a problem when the transmitter is removed then remove the transmitter from the plate assembly To test the transmitter see single Comanche service manual section 8 10 section 9 15 for twins connect an ohmmeter between the terminal and the housing and slowly move the float arm from the bottom stop to the top stop The ohmmeter indicator should steadily move up scale without fluctuation as the float arm is moved upward No drop a Copyright O 2009 International Comanche Society Inc All rights reserved 16 outs or opens are allowed If it isn t perfect proceed with the disassembly phase which is not covered in the service manual although the main subject of this writing Once you have determined necessity the disassembly method depends upon the type of transmitter you are investigating most employ the soldered rivet method some a cover with securing tabs 400 aux After disassembly you should first examine the wiper button condition If the wiper button is not serviceable your choice is a replacement transmitter If the wiper components pass inspection then use an ultr2. procedures appear to be necessary Some Suggestions The first step is to recognize the seriousness of the issue in terms of the potential that rust has on degrading the airworthiness of the fuel selector and hence the aircraft The other key issue is that these fuel selectors are a dead part as far as being able to replace a fuel selector body if yours corrodes beyond serviceability as did the one in the photograph There may be a few new old stock units available but these are limited and likely expensive Take care of your fuel selectors or lose them suspect that many owners are only performing ADs 79 12 08 and 83 10 01 at the annual inspection This is likely inadequate used to be a bit sloppy about draining the fuel bowls before flight That has changed In truth the fuel selectors should be drained after flight The longer water sits in the valve the more damage it will do The two ADs should also be performed religiously at 50 hour intervals as required It is probably a good idea to perform the ADs at least once every six months if the aircraft is not flying frequently When removing the fuel bowl to clean the filter as required by aD 83 10 01 go one step further After removing the fuel filter remove the little clip holding the bypass valve spring in position see photo a Copyright O 2009 International Comanche Society Inc All rights reserved 19 This allows me to remove the retaining washer spring and the byp
3. 24 2299 end up aed PA 24 260 SUED 10 72 PIPER COMANCHE SERVICE MANUAL cua New Fuel Pumps Relocated in Gascolator Compartment MI reat Are Easily Accessible mues TT aen atit z E E TRAA 26039 0 Cota PU ELE UT terran 20934 PUT N ct eS E N AS 37 a s US P Y amar sete ru LA A ane m E zz a ee CET Figure 2 6 Access Panels and Plates PA 24 180 PA 24 250 and PA 24 260 Serial Nos 24 4000 to 24 4246 24 4248 to 24 4299 E d Copyright 2009 International Comanche Society Inc All rights reserved 13 MOLIOR anci 3ud 003 44 M C TOLLA o NOLIVETHOREAN NOLIOGGSNI 24 96 E1 S a LI Torn 97 IA moge wer sup A82 7 OLA DILO Cl on TR san C on JO sa 3 tmi uva Om emt so PRIORY 3o sed qr P SUSE sape 9 srenjo ee li de II A vor3 uioguy pur ebuT u 293j sog 3uemjiedmo2 10391009 sua o3 1ucu 1w duos eS vH 013 dund eng OT1I9810 egy 93850191 Pe uo a AZOLLM 6662 PZON TWTIAS 052 PZNA zedta pipid e ai y2ngaad jo uertit pap pue ateni v nee pap sum ID BAHIA AD BdAL TAMANO o DAA MPI UL 100 OE Bue ooo revany fo paranas URI 1 Siem OD sdi arm dS i Sanin BIA FEN aecm2n wo p gt MOM IA A CETRO CIN Dd 2470 terme r wmaonpeig 01 monpa O i tenpan parar son CO au mj fs m our n E mornare jq PAN Nba es ajsagcus Meu Bus Menor eean rabo 7o BER povot Ai 80d jo seve enone ons es vei ihren muy jo a e BY yaya HECHT ODA IERIE IDA AT JO III NO
4. Annual inspection that is not on the inspection sheet The things that find that are missed are actually in the list but are either ignored or just missed know that have covered several items this past year but I ll give them all again here that way they are all together These are things have found that are very costly and if found early can save a lot of money and grief 1 Pull fuel plates off these are the ones that the fuel cap is under On the twins remove the cover plates located under the engine nacelle This requires removing the fairing around the nacelle Also remove the wrap around panel aft of the cowling With these items removed you can remove the fuel panels Under the panels you will find the fuel sending units This is where the problem lies If the gasket is torn or missing usually the latter water will get into this area and the corrosion process will begin keep Air Parts of Lockhaven busy repairing the fuel sending units If your fuel adapter isn t corroded too much this is the plate the fuel sender is attached to it might be cleaned up and reused The problem is that the fuel adapter usually is corroded to the point that pins holes are present These babies are getting very hard to find 2 On the twins again remove the small plate behind the top engine cowling Under this is the vacuum filter and cables have found many filters so old that when touched they fell apart and into pieces Also while yo
5. Bieck ICS 02171 One of Murphy s laws says If it is possible to install a part backwards someone will do so Recently when removed the sediment bowl from the strainer assembly part No 22312 00 in our 250 discovered internal leakage through the fuel selector valve hoof which later rectified by installing a new 0 ring What concerned me was that the fuel dribbled out of the outlet port above the screen To make sure it wasn t fuel draining from the line to the boost pumps selected a full tank and sure enough fuel streamed out of the wrong port then removed the strainer assembly from the aircraft Confirming what already knew the arrows on the casting showed that the outlet port was connected to the fuel selector and the inlet port 180 degrees opposite had the 45 degree fitting which connects the line to the fuel pumps and the engine Turning the unit 180 degrees and changing the fittings over to where they belong the right angle fitting receives the line from the fuel selector corrected the situation For 18 1 2 years we flew our Comanche with fuel flowing through the strainer the wrong way and feel embarrassed to admit this But then we never had leakage through the selector valve resulting in a dribble in the OFF position Neither did have a reason to take the strainer assembly out You can t see the arrows on the casting while the unit is installed except by using a mirror but never had reason to
6. FUT UM DOUE mary FO 20O8 IR HIV ERS hui boe emp Sinan os Sia rearaysey sesabar evt of FOODS ANANS 9 6 OFF PSION A sry AA apa n dear 9p wow RO BLVD DO BEAL Y E CE E 31Y21411822 34A 1Y LN3N3 1ddf YO 31211832 NOILINGOUS 31V21411432 AJAL 404 NOLLYIM dav OMOWIdV POI MOLLIS SIMMNO Y MCHCVUW TT MOUVLBOdTNYIL FO LAND 0 PT 20m uai weyeess o poysgiweo VU roi d prat io Sp 14 E d Copyright 2009 International Comanche Society Inc All rights reserved Test and Refurbish Procedure For Comanche Fuel Transmitters Apr 2006 Matt Kurke A amp P ICS 10288 If you are experiencing erroneous fuel quantity indications in your Comanche this may be of some interest and assistance in the diagnosis and repair of the fuel quantity indicating system This is not intended to replace the methods found in the service manuals nor to re hash them rather it is to offer additional information And obviously one should refer procedurally to the appropriate manual You determine if your capabilities include doing this yourself there isn t much mystery involved once the system is understood An error in fuel quantity indication can be caused by an incorrect resistance value being transmitted to the display gauge unit There can be a few sources for this problem Checking for poor connections should be your first line of diagnosis secondary would be a component One cause of incorrect resistance can be from corrosion where water
7. HQ a Copyright O 2009 International Comanche Society Inc All rights reserved 10 nz 425 5 m C E gt 2 m 1057 Y Original Fuel System Configuration with pumps hoses and connections all located of engine compartment Interrupter type fuel in lower aft section FAA APPROVED Gascolator Los z7 AIRCRAFT CERTIFICATION OF INITIALS War ge Prime iow Fuel Lines from Electric Pumps gine Driven Fuel Pump Ca retor New Electric Fuel Pumps Original Fuel Supply Lin wat New Bulkhead Fitting Original Bulkhead Fitting New Configuration New Fuel Supp Line Forward of rewall E d Copyright 2009 International Comanche Society Inc All rights reserved 11 o i i 90 Emow and Fittings As Mounted On Compartment ANS15 60 Nut ANBI9 60 Sieve Right Stringer Of Gascolator Fuel Pumps Diae Briven Piel Pump 22404 00 gh inel Fuel PIPER Tee E sdumd S009 oL 4ojoejeg jonj wold r 0s 8 9 pos rl TS 00754 magg MeAS t i prouJsujDSA 2613 06 QS 708NY dung jeni uerjig eujBus oj 28 3 06 09 Zz8NY 4ojoejes jen ui04j 966 5 T AVW O3A0UddY vd noqg S a9 CZENy uojjp4n5jjuo ipujbuo 104009509 eun Aiddns jeng p4D 40 4 wy upjoo mala dol 12 Copyright 2009 International Comanche Society Inc All rights reserved mam Original Firewall Location FIGURE 04 FUEL SYSTEM SCHEMATIC FUEL SYSTEM PA 24 250 Serici Nos
8. One switch and one C B for both and they are both wired together Good idea huh 13 On the 260 s the fuel pump is under the co pilot s floor just behind the rudder pedals For some reason this panel is not removed When removed there usually is a small fuel leak found 14 Check for fuel stains under the wing close to the wing root area 15 When changing oil filters replace the CH48110 with a CH48111 which is longer and holds more Last month covered this item and when received my issue found an error It should have stated that the CH48110 would bypass around 25 hours not 50 hours Costs the same but the CH48111 will last for 50 hours In addition remember it is important to change your oil every 3 4 months not just every 50 hours or sooner if operated in dusty conditions 16 Remove the Stabilator and check for corrosion find this on most of the birds that we inspect Continue to call me about this average about four calls per week on this matter About one out of five is clean and corrosion free 17 Please check this item It s AD 77 13 21 the notorious gear AD For some reason IA s are doing par b every 3 years or 500 hours and not par a They are signing off the AD as complete by doing par b Please check your logs and look for the completion of par a by inspection This is not considered complete by merely replacing the BUNGEES 18 On the twins remove the fuel filter bowls and clean If rust or
9. and if it turns by hand it is probably okay but the motor is a different matter There was a discussion on the Delphi site about the uniqueness of the new motor Weldon uses for the PA 30 pumps The pump has a tab on the shaft while the motor has a slot The end play tolerance between the tab and slot is critical If upon assembly the tab bottoms out on the slot the motor does not have enough torque to overcome the end play tightness One fix is to use the standard length motor make cutouts and bead them in the transverse shear web where the pumps are located Also the pressure needs to be set at 25 psi after the pump is installed There is one report of a series of pump failures more than six in all and these were all new Weldon units as supplied by Webco On disassembly of some of the older units it was found that the motors seem to run fine but the pumps have apparently seized When turned by hand the pumps turn okay and when reassembled they appear to work However there is still a problem and the pumps cannot be refitted without overhaul by an approved shop As this column is written there has been difficulty getting a response from Weldon on the warranty position Apparently with all the pump failures none have yet been returned to Webco or Aircraft Accessories and they can do nothing for warranty until the pumps come back It sounds like Catch 22 and until someone sends one of the failed pumps back to be disassembled a determination
10. cannot be made concerning the failures Water in the fuel of a hangared plane that is flown somewhat regularly seems strange It may have nothing to do with the pump failures but nevertheless the fuel caps and lid seals should be checked Also it should be noted if the water in fuel is coming from the left tanks only or distributed among all tanks left and right The water in the fuel could also be from your supplier If you buy your fuel regularly from the same place you might want to mention your water in fuel problem to the supplier and ask if there are any reports from others since it is an unusual condition Replacing amp Relocating the Electric Fuel Pumps An STC Apr 2003 Hugh J Gallagher Gallant Airmotive Inc To FAA am submitting form 81110 12 for a one time Supplemental Type Certificate This alteration replaces and relocates the electric fuel pumps The electric fuel pumps will be relocated from the right lower aft side of the engine compartment to the right stringer of the gascolator compartment in the belly of the fuselage In the PA 24 260 design the electric fuel pump is located in the belly of the fuselage The fuel System will not be changed in design Only the location and type of fuel pumps will change The pumps will be mounted on the right stringer and the stringer will be reinforced at the mounting location The pumps 2 will be new solid State type Facet 40106 12v solid State negative ground 4 6 p s i
11. has leaked into the transmitter area from poor sealing of an access cover Water collects in the depression where the transmitter unit is mounted take a look there EN ELO 5 um 2 This main tank transmitter didn t survive due to the extensive corrosion a Copyright O 2009 International Comanche Society Inc All rights reserved 15 Se eee te zd This wiper button is okay even with the small spot that has worn Another cause is internal to the transmitter a dirty resistance winding not obvious inside a fuel transmitter is quite common and easy to check The internals of the transmitter are simple and diagnosis and repair fairly simple once disassembled There are cases however where the fuel level transmitter has reached the end of its life i e the wiper button is too worn broken or missing or excessive housing corrosion A full range test must be 29 6 to 31 3 ohms for all except the Comanche 400 auxiliary transmitters they require two transmitters Before getting into the actual dissection of the transmitter take a moment to consider other possible culprits On the single models with one gauge display unit you will find four push button momentary switches and a rotary selector switch co located with the fuel tank selector Any of these electrical components may have developed some resistance which will add to the value from the fuel level transmitter the result will be erroneous fuel quantity indication
12. max 30 g p h with the same p s i and g p h as the original Bendix now Facet 478360 interrupter type Relocation of pumps will prevent pumps from heat soaking and possible vaporization of warm fuel causing low fuel pressures during hot weather operations These pumps are recommended by Rutan Aircraft Factory Stoddard Hamilton and other aircraft designers A new fuel line running parallel to the original fuel supply line will be extended from the electric fuel pumps in the gascolator compartment through a new Standard bulkhead fitting at the firewall and continue to the outlet side of the engine driven fuel pump The original fuel supply line will be extended from the firewall directly to the engine driven fuel pump with a new section of fuel line All work performed will be in accordance with acceptable methods and practices as per AC43 13 1A Chapter 1 Section 3 Para 99 Chapter 14 Section 2 Para 709 Chapter 11 Section 7 Para a Copyright O 2009 International Comanche Society Inc All rights reserved 9 514 515 516 and 519 Weight and balance and equipment list changes will be made and flight manual Supplements will be entered PA 24 250 S N 24 2999 was manufactured in 1962 Piper manufactured PA 24 250 Comanches from 1958 until the model was discontinued at the end of 1964 The PA 24 260 model started production in 1965 and continued until 1972 A significant improvement in the PA 24 280 model was the relocation of the ele
13. pump Old age and non use can cause these pumps to fail If your electric aux pumps are not working correctly i e able to supply the correct volume and pressure you may be faced with an engine failure See the TIPs Manual for advice on testing and ensuring correct pressure during maintenance Comanche Fuel Tanks Venting Feb 2004 Q How do the Comanche fuel tanks vent have heard there can be problems with the venting system What are the problems if any A The fuel caps on Comanches are not vented A blocked tank vent will therefore result in the fuel cell either not feeding or else the fuel cell being sucked flat Tip tanks can be deformed and collapse and rubber bladders will either be lifted upward or the cell will detach from the retainers and collapse from the top In either case the fuel quantity indicators will read incorrectly Comanche vent tubes mains aux s and tips have proven to be preferred homes for mud wasps It is a good idea to keep a length of flexible plastic tube in the aircraft and with the fuel cap off ensure that you can blow air into the tank It is a good idea to check the overflow at the same time keep a short length of old tachometer cable in my toolbox to run thru through the vents to clear blockage This is important especially prior to an Atlantic flight Fuel Tank Dipsticks Mar 2004 Q The fuel gauges in my Comanche 250 are not very accurate and when look in the tanks it is very hard to judge
14. the fuel level transmitter for tank position fuel tank Cleaned adjusted and tested the transmitter Re installed this serviceable unit with new gasket screws and seals Note You are the judge on this language Piper doesn t address repair of this component Some all work performed and using methods found in accordance with the Piper Comanche Service Manual 773 516 9th revision dated August 15 1998 An operational check was performed and found to be satisfactory Cancer Within the Care and Feeding of twin Comanche Fuel Selectors Feb 2008 Kristin A Winter ICS 15964 Much attention has been paid to the Comanche landing gear system and recently the condition of our tail feathers Another issue peculiar to the Twin Comanches made itself felt in Maggie my own PA 30 The first clue that all was not well in her fuel selectors was the presence of flecks of material which later discovered was rust appearing in the fuel samples had seen these before but was not overly concerned Even during the 50 hour when complied with AD 79 12 08 and AD 83 10 01 merely cleaned out the strainer bowl and investigated no further When one of my boost pumps gave up the ghost decided to replace both with the newer version STC d pumps With everything apart it seemed a good time to remove the fuel selectors and make a closer examination am glad that did What discovered was that the design of the valve body traps moisture tha
15. Tips from Comanche Flyer magazines Feb 2002 Aug 2009 CHAPTER THREE FUEL SYSTEM Table of Contents Fuel Selectors Feb 2008 isis iced accipe th id 2 Fuel Siphoning Problems Mar 2003 esee eene nennen 4 Fuel Selector Problems Mar 2008 ooooooccccccccccccccccnconononnnoononcnnnonncnnnnnccnnnnnnnnnnnns 4 Water Contamination in Fuel Filters Is Easily Avoidable Jan 2004 5 Electric Fuel Pumps Problems Feb 2004 c ccssecceeeeeeeeeeeeceeeeeeeeeeeeeeeeeeenees 5 Comanche Fuel Tanks Venting Feb 2004 esses 6 Fuel Tank Dipsticks Mar 2004 actas ai oan 6 Fuel Venting Overboard Mar 2004 ccocccccccccnccnnnconnnonnonnononoconnnnncnnccnncnnnnananons 6 Fuel Gauge Sender Unit Gasket Leaks June 2004 ssssssssse 7 Fuel Odor in the Cabin Jul 2000 ino tupvoeninndsbuentantcesteeiedvasesstavians 7 Engine Running Rough due to Clogged Fuel Injectors or Spider Aug 2004 8 Electric Fuel Pump Not Pumping Dec 2004 ooccoconinoninicicocoooconcnnnonnnoncnnccnninnnnnnn 8 Replacing Relocating the Electric Fuel Pumps An STC Apr 20093 9 Test and Refurbish Procedure For Comanche Fuel Transmitters Apr 2006 15 Cancer Within the Care and Feeding of twin Comanche Fuel Selectors Feb 2008h accu eau UD m E E UI 17 Fuel Cell Deterioration A Fuelish Tale Jul 2008
16. a sonic device employing a basic non acidic solution bath to clean the wound resistor element The ultra sonic bath device is a Harbor Freight item alternatively they can commonly be found in the female s area of the bathroom Don t tell her you used it to clean your fuel injectors Remember the end result of approximately O to 30 ohms is required The 400 Comanche auxiliary transmitters are 15 ohms each because the aux tanks require two transmitters which are connected in series Be sure to repeat the test procedure after you have cleaned a transmitter To mechanically reattach the pieces of the transmitter try using a compression riveter on copper rivets I bought them from McMaster Carr The rivets will need to be annealed prior to squeezing If everything is clean with no corrosion you should be able to solder the rivets to assure a seal and no fuel leaks If you re not interested in purchasing 100 lot quantities kits are available The kit includes five sealing washers one gasket five SS screws two copper rivets two PVC sleeving one brass nut and washer And if you don t like the condition of the wiring in the wing a few feet of 18 gauge MS22759 16 Tefzel amp wire can be used to splice onto the existing inside the wing The wire kit comes with butt connectors heat shrink tubing a grommet and ring and knife terminals already crimped If you do decide to take on this task yourself this is what suggest for a logbook entry Removed
17. ass valve itself Then place a pail or other catch basin under the selectors and get into the aircraft By switching the selector from OFF to MAIN the AUX and the Crossfeed for each tank drain fuel through the bypass as well as the normal pathway This hope will help flush some of the water droplets which seem to accumulate above the divider between the upper and lower chambers and the water trapped between the bypass valve and underside of the divider have not figured out how to test this technique so don t know if it offers significant benefit At least the effort is very modest It is likely that as further time passes more of these selector bodies will become unserviceable The day may come where no serviceable replacement is available The solution would be to design and gain approval for a replacement body made of stainless steel Once the Comanche community has addressed the horn issue the Twin Comanche fuel selectors may merit our attention Regulatory Requirements ADs 79 12 08 and 83 10 01 address the condition of the fuel selector These are recurrent ADs They are required at a minimum of 50 hour intervals and portions of AD 79 12 08 are required as part of routine operations AD 79 12 08 incorporates Piper Service Letter 851 It addresses two issues The first addressed in Part A of SL 851 deals with seal leakage which can cause fuel to shift from tank to tank or lead to a certain amount of air being pulled in to th
18. be suspicious We never had a problem but think we were very lucky If we had ever gotten a load of dirty fuel all the crud would have been trapped on top of the screen possibly blocking it No wonder we never found anything bad in the samples we have been taking all these years Also never found anything that caught my attention on top of the screen during annual inspections or would have caught on Before we brought our 250 in 1975 it was operated and maintained by a Piper dealer We never had occasion to remove the strainer from the aircraft and the dealer probably didn t either Did the aircraft come like that from the factory or did the mistake occur during a subsequent repair or modification We will never know Most of the early records were lost in a hangar fire long before we bought the aircraft and the surviving records do not give any clues a Copyright O 2009 International Comanche Society Inc All rights reserved 4 Water Contamination in Fuel Filters Is Easily Avoidable Jan 2004 Mike Rohrer ICS 13393 was just reading an article in the December issue of Flying magazine on a topic that have written about several times guess it still isn t getting across We need to take care of these machines so that they will take care of us In addition this is one of the reasons that our insurance rates are going up Did you know that some companies are not insuring Twin Comanches that are older than 1965 And some are
19. ctric fuel pumps from the engine compartment into the fuselage away from any heat source Therefore the alteration am applying for is an improvement that Piper made on the later PA 24 260 model aircraft and will improve the safety and Performance of the PA 24 250 model aircraft am submitting schematics of the PA 24 250 and the PA 24 260 fuel Systems a drawing of the new fuel System showing location of pumps lines and fittings copies of weight and balance changes equipment list changes and flight manual Supplements Thank you for your time and attention in this matter Dear Mr Gallagher Approval of Fuel Pump Installation Modification in a Piper PA24 250 Model Aircraft Serial Number 24 2999 Project No ST4209LB A We have reviewed the data submitted by the above referenced letters from Mr Michael Ross the aircraft owner and find them acceptable Also Mr VanDyke of this office inspected the aircraft Installation at the Palomar Airport reference 3 and found it to be satisfactory Therefore we are issuing Supplemental type Certificate STC SA00198LAtoyou Also enclosed is a stamped approved copy of your engineering Master Data Report 92024 dated May 13 1996 This STC is applicable to Piper Aircraft Serial Number 24 2999 only If at some future date you wish to obtain a multiple i e applicable to more than this one aircraft STC you will need to reapply at that time In accordance with Federal Aviation Regulations 821 3 a
20. d there would have been no requirement to check the inside of the fuel cells ever Not having changed the vents may have saved our lives Imagine the irony of that 2 Always have half an hour of gas in a tank that you can go back to 3 Don t ever ignore basic maintenance That 100 000 radio stack won t save your hide if the prop stops turning It is our understanding that we could legally have sent these old fuels cells out for overhaul again Did we Absolutely not We destroyed them and bought new ones Ae Copyright 2009 International Comanche Society Inc All rights reserved 23
21. e engine Comanches the 1966 and later models have fuel injected engines and the symptoms you describe are not uncommon Our panel of technical experts suggests you have at least one blocked injector or foreign material in the fuel distributor spider possibly both As a result one or more of your cylinders is not receiving proper fuel flow and is running too lean That is why leaning makes it worse you are already too lean on one or more cylinders The fuel flow which you think is rising is not doing so The fuel flow gauge is actually a pressure gauge calibrated in fuel flow units With an obstruction increasing the back pressure in the fuel system you have an indicated rise in fuel flow not an actual rise While the problem could possibly be isolated with an engine analyzer it is probably best to clean the entire System The injectors the fuel spider and the related lines should be cleaned and the small strainer from the fuel servo should be checked for contamination and corrosion Another good bit of advice is to have a look at the top of the piston and underside of the valves in the affected cylinder to make sure there is no damage caused by running lean at high power for a prolonged period One member with a 1966 260B removes and ultrasonic cleans his injectors every 200 hours as a matter of routine maintenance since all the injectors become dirty with use This can be caused by fuel dye and other additives in the fuel He says he i
22. e fuel line if the tank with the leaky port happens to be empty Compliance involves positioning the fuel selector valve to off and checking to see if the valve continues to drip fuel Compliance with Part A is required every 50 hours Part B of SL 851 concerns ensuring that any water is eliminated from the fuel system The procedure specified in Part B has been incorporated into the updated pilot s manuals AD 79 12 08 requires draining the sumps through the required procedure if the aircraft has been exposed to freezing temperatures This means that if you are flying at an altitude that is below the freezing level the pilot is required by the AD to drain the sumps before the first flight of the day and after refueling AD 83 10 01 concerns solid contamination in the fuel by requiring that the fuel filter be cleaned every 50 hours a Copyright O 2009 International Comanche Society Inc All rights reserved 20 Fuel Cell Deterioration A Fuelish Tale Jul 2008 Don Ostergard ICS 3263 Our sturdy bird was recently in for its annual It is a 1959 PA24 250 which makes it 49 years old We ve owned it since 1979 almost 29 years It is equipped with the standard for 1959 two 30 U S gallon inboard fuel bladders some folks call them fuel cells It also has tip tanks that are of no consequence to the following story Back in 1988 20 years ago we became aware of fuel stains under the inboard area of the wings as well as the
23. e patches all choose to loosen up more or less simultaneously after 19 plus years is somewhat of a mystery but is beside the point It takes very little imagination to visualize one of these patches falling off and blocking the fuel outlet one s bones go soft just thinking about it a Copyright O 2009 International Comanche Society Inc All rights reserved 21 The photo shows one of the fuel cells and the fifteen patches that it contained There were patches on the patches The other fuel cell wasn t any different We must stress that the repairs to these fuel cells were in full compliance with approved recognized practices Everything was perfectly legal Summary To recap The plane was built in 1959 we bought the plane in 1979 The fuel cells may have been overhauled sometime during the period 1959 1979 we haven t bothered to check the old records We do know that they were overhauled once between 1979 and the present namely in 1986 We are fanatic about maintenance There have been no maintenance shortcuts taken with this plane in the past 29 years There has never been anything but avgas in the tanks If this happened to us it can happen to anyone Ae Copyright 2009 International Comanche Society Inc All rights reserved 22 bp Can We Learn From This Be sure to check those fuel cells regularly You can do it yourself in a few minutes using a flashlight and a mirror If our plane had the new style vents installe
24. fuel What is happening a Copyright O 2009 International Comanche Society Inc All rights reserved 6 A Although you didn t say so assume your twin has tip tanks The fuel system is designed so that the lines from the tip tank and the aux tank both feed into a solenoid valve The switch near the tank selector switches the solenoid valve so the fuel feeds from the tip or the aux tank If the o ring is bad in the solenoid valve or if there is a bit of debris lodged against the valve seat fuel will drain from the tip tank to the aux tank through the solenoid valve since the tip tank is higher Your aircraft is not manufacturing fuel The fuel is simply transferring from the tip tank to the aux tank When the aux tank cannot hold more than its capacity the excess vents overboard You need to remove the solenoid valve for inspection Both solenoids are located in the cabin against the front of the main spar Fuel Gauge Sender Unit Gasket Leaks June 2004 Q When fill the right auxiliary tank on my twin after landing find a blue fuel stain that seems to be coming from a panel behind the tank fill door What is under there that could be leaking and how do fix it A The panel you refer to is where the bladder is installed It is also the location of the fuel quantity sending unit The cork gasket on the sending unit tends to dry out after time and if the tank is full there can be leakage during climb out Usually you ca
25. he cut away photo that the design of the divider between the upper and lower chamber has a tendency to trap droplets of water both above the divider and on the lower side of the divider between it and the seat of the bypass valve Sooner or later the droplets of water will overcome the cadmium plating on the selector body and rust will form a Copyright O 2009 International Comanche Society Inc All rights reserved 18 FUEL SELECTOR BODY CUT AWAY In hindsight it seems that making the body out of cadmium plated steel was inadequate to withstand the water that was bound to accumulate The fact that an earlier service bulletin required the replacement of the cadmium plated bowl with one made of stainless steel is evidence that the potential for internal corrosion was not sufficiently taken into account in the design This occurred after little more than five years in service The follow on airworthiness Directives are further testimony to the potentially serious nature of the problem Besides potentially degrading the fuel selector to the point of being unserviceable the accumulation of rust has the potential to clog fuel injector nozzles Rust particles also have the potential to lodge in the seat of the ball check valves causing leakage and transferring of fuel from one tank to the other Given the clear airworthiness implications and the seeming pervasiveness of the problem of corrosion in the Pa 30 fuel selectors improved maintenance
26. how much fuel there is Lots of times have a short trip that doesn t require a lot of fuel but with four people aboard don t want to fill the tanks to the top Yet by just looking in the tank sometimes l m not certain if there is enough fuel Is there a way to measure the fuel A Years ago made a dipstick for my 250 just to address the very concerns you expressed used a piece of white oak any dense wood will work and with a tank that had run empty added 5 gallons at a time and measured the result See accompanying photos One side of the stick is for the mains the other for the auxiliary tanks made the marks with a saw and painted the stick flat black For 5 and 10 gallons in the aux tank the marks are at 29 16 inches and 4 5 16 inches The main tank markings in 5 gallon increments are 2 inches 3 1 2 inches 4 5 8 inches 5 3 4 inches and 7 1 8 inches now use the same stick for my Twin Comanche Of course the aircraft needs to be level for the readings to be valid Fuel Venting Overboard Mar 2004 Q have a twin Comanche Occasionally will find fuel going overboard via the vent line from my right auxiliary tank It is as though the tank is being overfilled even though it is not have been careful to not fill the tank to maximum and still sometimes there will be fuel dripping from the overflow after the aircraft has been sitting for some time Is my airplane haunted It seems to be manufacturing
27. is is the result of a rusted check valve in the selectors which does not seat anymore Therefore fuel passes through into another tank So please for safety sake drain your tanks Airplanes get very quiet when the fuel flow stops It is so easy to drain so why take the chance It doesn t make any sense to me Electric Fuel Pumps Problems Feb 2004 Q Occasionally the engine on my 250 sputters and wants to quit after takeoff when switch off the electric fuel pumps The pressure indicates it is low when this occurs but goes back up when I switch the electric pumps back on Is my engine driven pump going bad A The plumbing of the aux pump on 180s and 250s is configured so that while the aux pump is on fuel is not flowing through the engine driven pump and the fuel in the engine driven pump rapidly heats This can result in a vapour lock in the pump and an engine stoppage when the electric pumps fails or is turned off It is recommended that the aux pump is checked as part of pre flight and then not turned on until immediately prior to takeoff It should be off during the engine run ups to prove the efficiency of the engine driven pump Vapour lock is usually a concern only during the hot summer months Also here is some additional information concerning your engine driven pump Ae Copyright 2009 International Comanche Society Inc All rights reserved 5 Most normally aspirated Comanches use a diaphragm type engine driven fuel
28. letin is a simple fix that largely removes the risk of the vent plugging when flying in icing conditions It is likely that almost every Comanche in existence has had this procedure performed on it To comply with the later AD one may either install a different fuel venting system very expensive high labour component or simply check the vent tubes for obstructions and inspect the fuel bladder internally every 100 flight hours This inspection to reduce it into the simplest terms consists primarily of inserting a small mirror through the fuel filler neck and shining a flashlight into the bladder to see if the bladder has collapsed unsnapped It takes about five minutes per tank to perform this inspection The sturdy bird does not have the modified fuel vent so it undergoes the 100 hour inspection No big deal Our AME we call them Aircraft Maintenance Engineers here in Canada they re known as A amp Ps in the U S has done it at least 28 times One could perform the inspection oneself every time the plane is refuelled if one wished It might actually not be all that bad an idea In the course of this latest inspection our AME discovered a big patch hanging down from the top of one fuel cell Then he checked the other fuel cell Same thing We are not making this up So he removed the oval access plates reached his hand inside and ran it inside the top of each fuel cell Imagine his surprise when patches started falling off in his hand Why thes
29. n resolve the leak if you remove the sending unit and apply Fuel Lube to both sides of the cork gasket Fuel Lube is a Vaseline like substance available from Aircraft Spruce p n 09 25300 Also be sure to apply a sealant to the edges of the cover to keep water out of the cavity If water gets into the cavity corrosion can occur on the bolts that retain the bladder and cause leakage around the bladder retaining plate There is more than one choice for a sealant One is aviation grade RTV which is an approved aircraft sealant compound but you must be very careful when using it especially on fuel systems Unlike Fuel Lube some RTV can harden and become brittle Small pieces could cause a blockage if they get in your fuel system An alternative to aviation grade RTV is a non hardening sealant used by some of our members Sealube by Ohio Industrial Lubricants A one pound can from Aircraft Spruce will last forever Fuel Odor in the Cabin Jul 2004 Q have a 1967 PA 30 There is an occasional fuel smell in the cabin We have checked all the fuel lines in the cabin along with the fuel selector and the boost pumps We can t find the leak Any ideas A If there is even a tiny leak in one of the fuel bladders the fuel smell can migrate to the cabin thru the wing root and is often especially apparent after landing The most common place for small holes to develop is in the top of the bladders main or aux tanks In this case the fuel smell is prese
30. nd as a recipient o this certificate you are required t report any failure malfunction or defect except as provided in 21 3 d J in any product or part manufactured b you or your contracted suppliers and which you have determined h resulted or could result in an occurrences listed in 21 3 c The report should be communicated initially by telephone to the Manager Propulsion Branch Los Angel Aircraft Certification Office Phone No 310 627 5241 within 24 hours after it has been determined a fail has occurred and followed up with written notice to the address show above FAA Form 8010 4 malfunction or defect report or other appropriate format is acceptable in transmitting the required detail You as the STC holder responsible for any design changes necessary to correct unsafe conditions as well as for submitting those design changes to this office for approval This requirement is contained in 821 99 In addition you are required to advise this office of any change in address Also 821 50 requires that maintenance procedures for continued airworthiness as applicable to this change in type design be made available to the Operator at the time the aircraft is returned to Service By accepting this certificate you acknowledge that you have read and understand your responsibilities as STC holder Editor s Note This is only a portion of the Information there is too much to print For more details on this time STC please contact
31. not even covering the Comanche 180 s The Flying article states that a Twin Comanche lost power in both engines and crashed due to ice build up in the fuel filters Come on people there is an AD that covers this and it s due every 50 hours It states To eliminate water contamination of the aircraft fuel supply and mandates compliance every 50 hours of operation This aircraft had not been complied with in 16 calendar months and 234 hours of operation Basically the AD wants you to remove the filter bowls and check for water every 50 hours The Owner s Handbook states auxiliary fuel and tip tank fuel should be used in level flight only Examination of the wreckage revealed evidence of fuel at the scene with the left fuel selector in the auxiliary position and the right selector in the main position The airplane was in cruise flight at 6 000 feet in below zero temperatures know that not everyone checks his or her fuel filters but at least drain the things 20 to 30 seconds for each tank go as far as draining them after flight This way if any water is trapped when first drained it most likely will be repositioned after flying continue to see water in the filter bowls in twins some so bad that the selector had to be overhauled because of severe corrosion A sign of corrosion is when you go out to the airplane after it has sat and when you remove a fuel cap the fuel gushes out and one of your other tanks is low Th
32. nt when the tanks are full but not when they are down a bit Another site for fuel leaks is in the fuel sender fittings in the tanks These may become corroded if the overlying inspection panel has not been correctly sealed allowing water ingress Another source of a fuel leak could be the combustion heater John Regier at Webco reports that they have lately found a couple of cases where the fuel leaks slightly around the valve stem but only when the valve is being operated That situation would make the leak difficult to locate Check that the lines are not reversed to the valve The valve stem seal should not be pressurized when the valve is off but this will occur if the lines are reversed as they can be a Copyright O 2009 International Comanche Society Inc All rights reserved 7 While you say that you have checked all the fuel lines the fittings on these lines can actually leak without any visible evidence of a fuel stain Someone familiar with them should check them Do not just tighten them further This can crack them Some of these fittings require small o rings which should be present and in good condition Engine Running Rough due to Clogged Fuel Injectors or Spider Aug 2004 Q have a 1966 260 B Model Comanche Lately the engine is running a little rough and have noticed the fuel flow is higher than normal What do you suppose is causing this Leaning doesn t help it gets worse A Unlike the earlier carbureted singl
33. occasional whiff of gasoline fumes in the cockpit Clearly the main fuel cells were beginning to seep So as the logbook entry states out they went for overhaul at a repair shop that is licensed to repair overhaul fuel cells We were in on the decision and remember it well Now it is always the top surface of a fuel cell that dries out and starts leaking When a fuel cell is sent out to the repair facility for overhaul they will pressure it up find the leaks then turn the cell inside out and cement patches onto the offending spots pressure test again and return the fuel cell to service In most cases there will be several patches involved along with multiple retests before the last leak is repaired The bladders were overhauled replaced in the wings and gave nearly 20 years of excellent service There was never a trace of fuel seepage and never a whiff of gas fumes in the cabin Shortly after the Comanche was introduced 50 years ago there were apparently some instances of the fuel vent tubes which are located on the underside of the wings and face forward becoming blocked with ice when the aircraft was being operated in icing conditions With no opportunity to vent the bladder to compensate for the fuel being consumed in flight the bladder would of course collapse upon itself popping some or all of the snaps that were holding it in place Service Bulletin 190 June 1960 and AD 68 13 03 1968 address this issue The Service Bul
34. s amazed at the difference in performance with clean injectors Electric Fuel Pump Not Pumping Dec 2004 Q have replaced two left electric fuel pumps this year and the third one just failed Always the left one One was old one was new from Weldon and the last one was overhauled by Aircraft Accessories The aircraft is hangared in south Florida and the fuel is sumped every flight We usually get a teaspoon of water from 6 tanks We have installed reminder lights for the pumps and do not leave them on except as required Any suggestion would be greatly appreciated A We re sorry to say you may have stumped the experts but let s give it a whirl The fuel pump situation sounds onerous and the fact it is always the left one that fails does not suggest a quality problem with the pumps although it doesn t rule it out Definitely the pump manufacturer should be contacted and an inquiry as to the possible causes for pump failures The answers should give a clue as to where to start looking for the problem Repetitive pump failure sounds as if the pump may be working too hard The fact that each failure has involved a different condition pump i e used old a new Weldon and now an overhauled one from AA is puzzling There may be something else going on You might check the fuel lines and make sure they are unobstructed a Copyright O 2009 International Comanche Society Inc All rights reserved 8 The pump itself has hardened steel vanes
35. sand is found you are not draining enough This will in time cost you a lot of money to overhaul the fuel selector valve and if you are lucky it will not kill you or destroy your airplane when the engine shuts down because of fuel starvation have found a great place to have the selector valve overhauled George down at AirParts of Lockhaven in PA does a wonderful job and provides a quick turnaround 19 The fuel bowls on the PA24 s are equally important a Copyright O 2009 International Comanche Society Inc All rights reserved 3 20 Check the nose strut where the turning stops are located The stop should have a shoulder on it and not worn off and check real close for cracks The damage is caused from turning the nose gear beyond the stops Call and I ll send you the turn limit decal Fuel Siphoning Problems Mar 2003 Mike Rohrer ICS 13392 Recently while investigating a complaint on a PA30 fuel siphoning problem found that the fuel selector was by passing through The left aux tank was leaking into the right main tank When removed the fuel bowls for the inspection found what had expected There was a lot of sand and water in the bowls and when the fuel selector was removed found the check balls were leaking through because of corrosion The selector could not be overhauled and a serviceable unit had to be purchased Moral of the story drain drain and drain some more Fuel Selector Problems Mar 2003 Al
36. sesessssse 21 a Copyright O 2009 International Comanche Society Inc All rights reserved Fuel Selectors Feb 2003 Mike Rohrer ICS 13392 This month would like to address an old AD that has been around since 1970 AD 70 22 02 covers the Airborne fuel selector in our PA 30 39 s don t know why but have found two PA30 s and one PA39 that this AD was not complied with In short this AD addresses the selector valve What you are looking for is a roll pin retaining sleeve and safety spring clip to insure a more positive means of securing the fuel selector valve control arm roll pin Look for the valve model number This can be found on the manufacturer s plate Open the door between the front seats where the fuel quick drain is located Under the model number is another set of numbers and letters If the number is 4 R 5 R etc and subsequent letter codes the valve is not affected by this AD The purpose of this AD is to prevent the possibility of engine fuel starvation resulting from the inability to operate the fuel selector valve due to loss of the control arm roll pin If your valve is covered by this AD and has not been completed a red dot should be located on the fuel selector arm immediately adjacent to the retaining sleeve Piper Service Bulletin 314A also covers this AD Contact your IA if you have any question or feel free to contact me I ll fax you a copy of both have received many calls about what to look for during an
37. t is not drained during normal pre flight or even when drained using the mandated procedure which calls for 10 25 seconds of draining per tank This water had in turn caused rust to form in the divider area between the upper and lower chambers of the valve Fortunately for me my selectors were not as badly corroded as the one shown in the photograph Ae Copyright 2009 International Comanche Society Inc All rights reserved 17 Corroded fuel selector body From the comments of others on the Comanche Flyer forum and on the Delphi forum numerous other Twin Comanche owners have found rust in their fuel selectors Based on the obvious design issues regarding the fuel selector itself it appears that this may be a fleet wide problem Operation of the Fuel Selector In normal mode the fuel selector operates by porting the fuel into the upper chamber of the body The position of the selector determines which of the ball check valves is pushed open From the upper chamber the fuel flows down the center tube into the stainless steel fuel bowl The fuel then travels steel fuel bowl The fuel then travels up through the filter into the lower chamber and up out of the outlet In the bypass mode the pressure differential created by a clogged filter will pull down the bypass valve allowing fuel to flow from the upper chamber through the four holes into the top of the lower chamber and through the outlet port It is easy to tell from t
38. th some sort of penitrant spray Let it soak for a while drink a coke or if you smoke have one The oil will seep through if there is a crack have found cracks that were not visible to the eye Once cleaned up by sandblasting it showed up 8 With the exhaust removed look into the exhaust ports and between the fins located next to the exhaust ports You will see a fine line that is white or black Looks like a carbon crack for those who have seen those before Also suggest spraying dye penitrant into the exhaust port and then wait If it s cracked it will show up between the fins have found that cylinders that were overhauled and have about 600 800 hours usually have cracks 9 Remove the gear jackscrew and motor assembly This is cleaned and lubed just like the flap assembly 10 Remove the mags both Slick and Bendix type Check the condition of the points and adjust per manufacturer specifications 11 On the PA24 s remove the fuel selector valve clean and lube This takes a special type of lube If your IA doesn t have it call and will send you some can t see buying a can you will never use it all in your lifetime or your kids for that matter Use it sparingly if not it will show up later in your fuel filter Trust me on this 12 On the 250 s make sure that the fuel pumps electrical are disconnected from each other and checked individually You will be surprised how many have found where only one is working
39. u have this plate off please lube the cables Now is the time when cables get very stiff and if forced will break What a nightmare this is Call and will sell you the best can of lube that have found to break free stubborn stiff cables have not found one yet that had to be changed due to this problem 3 Check tension on all control cables Did you know that if you have an autopilot and are having problems with the Altitude hold doing a little roller coaster maneuver most times it is the cable tension 4 Turn on the autopilot What you want to do is put opposite pressure on the controls for example if the control wheel is turning to the left hold it and turn to the right Just slight pressure and do the same with the pitch What this does is clean the discs in the clutch pack You would be surprised if you knew that most autopilots would not disengage if a need rises Autopilots are made to disengage with a certain amount of force in an emergency 5 Remove the flap jackscrew and motor assembly This is very seldom done remove it every 500 hours clean remove the end cap and clean out the old grease and install fresh a Copyright O 2009 International Comanche Society Inc All rights reserved 2 6 Remove and clean the fuel injector This is another item that is missed soak them in gun cleaning solution while in an ultrasonic cleaner If you don t have one just soak them 7 With the exhaust removed spray the welds wi
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