airman57 Posted April 20, 2008 Share Posted April 20, 2008 OUR ENGINES ARE T56A15. SOMETIMES WHILE STARTING, ENGINE RPM IS STAGNATION SOMETIMES AT %10 RPM------------(NO FUEL FLOW) SOMETIMES AT %40 RPM------------(YES FUEL FLOW) SOMETIMES AT %50 RPM ALSO TIT AND FUEL FLOW IS STAGNATE.---(AT YES FUEL FLOW) BUT THIS PROBLEMS DO NOT OCCUR EVERY START (EVERY TIME) WE CHANGED: STARTER CONTROL VALVE STARTER ENGINE BLEED AIR VALVE (AT FIREWALL) STARTER BUTTON (AT FLIGHT DECK) CHECKED BLEED AIR DUCT FOR AIR LEAK. CHECKED ELECTR.CABLE PROBLEM IS CONTINUE FROM TIME TO TIME. CAN YOU HELP ME? FOR YOUR ADVISE.THANK YOU EVERYTHING. Quote Link to comment Share on other sites More sharing options...
airman57 Posted April 20, 2008 Author Share Posted April 20, 2008 ALSO WE CHANCED COMPRESSOR BLEED AIR CHECK VALVE AND ENGINE BLEED AIR VALVES (5. AND 10.) Quote Link to comment Share on other sites More sharing options...
Steve1300 Posted April 20, 2008 Share Posted April 20, 2008 IT would be helpful to know things like outside air temperature, your altitude, and the TIT and RPM when the stagnation occurs. Also, are you trying the start in \"null\" as well as \"auto.\" Where is your null orifice on the TD valve set to? If it is an APU/GTC start, what is your bleed air pressure duing rotation? Have you tried it with another engine as the bleed air source? With everything you have changed, there isn\'t much left other than the fuel control itself. Quote Link to comment Share on other sites More sharing options...
pjvr99 Posted April 21, 2008 Share Posted April 21, 2008 As the stagnation seems intermittent, there may be several different issues involved. Stagnation at 10% may be a failing/failed starter; while at 40%/50% sounds like bleed vlaves closed, although this would need to be confirmed by null/auto start TIT\'s. Also What is the bleed manifold pressure during start? You may have a bad load control valve on the GTC. Quote Link to comment Share on other sites More sharing options...
Lkuest Posted April 21, 2008 Share Posted April 21, 2008 On top of all the good suggestions, double check rigging. Usually before engine start, the propeller blade angle is anywhere between 6 and 10 degrees on the protractor. If it is excessive, move the blade angles to reverse, then move them back to ground idle. Assuming the linkage part of the rigging is correct, the blade angle for ground idle should be between 5 and 6 degrees if you move the blades youself. A 10% hang is usually a bleed air problem. If the manifold pressure drops down really low, say 5-10 psi, the engine is taking all the air that is provided, and the GTC isn\'t providing enough air. If the manifold pressure barely drops, the engine isn\'t taking the air that the GTC is giving it. If manifold pressure stays high, you can remove the starter sensing line from the starter control valve and cap the line and fitting off. This will force the starter control valve full open (only for troubleshooting purposes.) Another thing to do would be to start the affected motor up, then while it is running, check for leaks at all bleed air ducts. Also, ensure the anti-ice valves are closed by doing the LSGI anti-ice check. To test the speed valve, simply disconnect the speed valve and cap off the line and fitting. If it immediately starts easier, the speed valve is bad. Quote Link to comment Share on other sites More sharing options...
APUnit Posted April 21, 2008 Share Posted April 21, 2008 How about checking either the fuel control or the atomizer? It might either be both? Also bad ATM maybe? Keep ALCO in mind if you need an APU fixed :) Quote Link to comment Share on other sites More sharing options...
airman57 Posted April 21, 2008 Author Share Posted April 21, 2008 OUR AIRCRAFT HAVE GTC.OUR GTC IS GOOD. BECAUSE GTC MANIFOLD PRESSURE IS 42-43 PSI.(AT THE BLEED GAGE) GTC MANIFOLD PRESSURE DROPS 26 PSI DURING ENGINE ROTATION (WHEN PUSHED THE STARTER BUTTON,FISTLY) THEN IT STAYS 30 PSI DURING ENGINE STARTING CYCLE.THIS CONDITION IS NORMAL.BUT ENGINE STAGNATION AT %10 RPM.(SOMETIMES)(IT IS NOT EVERYTIME),(IT IS NOT ALWAYS)(THIS FAILURE DOES NOT OCCUR ALWAYS.) FOR EXAMPLE AIRCRAFT IS FLYING AT THE DIFFERENT LOCATIONS.(IN ALL 8-10 SORTIE)WE SEE THIS FAILURE ONE TIME OR WE DON\'T SEE THIS FAILURE. AIRCRAFT FLY FOR DAYS,NO PROBLEM. BUT SOMETIMES THIS FAILURE OCCUR AND I AM FEELING BAD THINGS AT THIS TIME.IF THIS PROBLEM OCCURS ALWAYS I WILL SOLVE THIS ENGINE PROBLEM. NO FUEL FLOW,NO IGNITION,NO TIT AT %10 RPM.BECAUSE OF THIS REASON IT IS NOT IMPORTANT------(TRYING THE START \'\'NULL\'\'OR \'\'AUTO\'\')IT IS NOT FUEL SYSTEM FAILURE OR T/D SYST.FAILURE.IT SEEMS THAT A BLEED AIR PROBLEM. WE CHECKED PROPELLER BLADE ANGLE. GROUND IDLE ANGLE:5 DEGREES WE TRIED TO START ANOTHER ENGINE BLEED SOURCE AT HSGI.SOMETIMES SAME PROBLEM WAS OCCUR,SOMETIMES IT WAS NOT OCCUR.OUTSIDE AIR TEMP.18 C DEGREES,ALTITUDE 2800 FEET.IT WAS OCCUR AT SEA LEVEL TOO. Quote Link to comment Share on other sites More sharing options...
pjvr99 Posted April 22, 2008 Share Posted April 22, 2008 Ok, that\'s good info. Seems we have 2 possible areas where we can look..... 1. Check bleed sensing lines from starter motor to starter valve for damage/ leaks 2. Check the 1-way bleed-air check valve. The flapper seats and hinges become worn and do not seat properly, or stick in part open positions reducing the amount of air available during starting. I have had 4 or 5 of these in the last 12 months ..... This may be a silly question, but have you checked magnetic plugs? It may be an idea to pull the lower plugs on both the ADH and RGB to heck for debris ..... Quote Link to comment Share on other sites More sharing options...
Gmon Posted April 23, 2008 Share Posted April 23, 2008 The starter sensing line sounds like a good shot, given the details. I would get new elbows on both ends. I know you have only one set of eyes, but what is the manifold pressure doing when it hangs up? How do the C/Ps on the starter control valve and bleed air valve look? Sounds like the gremlin named Random. Quote Link to comment Share on other sites More sharing options...
Steve1300 Posted May 1, 2008 Share Posted May 1, 2008 I am still hoping that the solution to this problem gets posted here. Are there any results on the troubleshooting yet? Quote Link to comment Share on other sites More sharing options...
pjvr99 Posted May 1, 2008 Share Posted May 1, 2008 Seems to be a common problem - people ask for advice, and then don\'t bother to debrief ..... :ohmy: :huh: Quote Link to comment Share on other sites More sharing options...
airman57 Posted May 3, 2008 Author Share Posted May 3, 2008 EXCUSE ME.I AM TOO LATE. OUR PROBLEM IS OK.NOW. FINALY,WE CHANGED STARTER BUTTON AGAIN. (MAY BE) FAILURE WILL OCCUR AGAIN.BECUSE FAILURE DOSEN\'T OCCURE EVERY TIME.THANK YOU FOR YOUR ADVICE. THANK YOU VERY VERY MUCH..... Steve1300 pjvr99 Gmon Lkuest APUnit I WILL WRITE TO YOU IF OUR FAILURE OCCURS AGAIN. SEE YOU LATER. BYE.... Quote Link to comment Share on other sites More sharing options...
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