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#4 eng wind down in normal speed, restart FF stagnant, rpm stagnant, TIT exceed 850.


edwardlcy
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Hi guys, would like to share my defect with you and hope for some suggestion s:

As stated, #4 eng wind down during line up in normal speed, subsequent restarts found Fuel flow stagnant at 350 inlbs, rpm stagnant at around 40%, but tit keep increasing and forced to stop start due to over temp, happens when start with TD in auto and null..

I have already adjusted blade angle, jump triple S, replaced td valve but defect still persist..

What else should I look at? Could it be compressor stall? I'm at FOB with limited facilities, hope you guys can throw me a lifeline tq.

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Open the clamshell doors and see if the 5th and 10th bleed valves are closed. You may also want to push a borescope probe through the bleed collectors to inspect the top and bottom valves. If they are closed, think Speed Sensitive Valve failure. I have also had the Accessory Drive Housing cause the speed sensitive valve to fail. When changing the Speed Valve, I recommend draining the Accessory Drive to both lower the level of oil in the casing, as well as visually inspecting the drain plug for metal.

Your defect cannot be fuel related because high TIT would cause a faster start, and low TIT would cause a slower start. They go hand-in-hand. If you suspect low-starter air pressure, disconnect the starter sensing line to force the starter control valve to stay full-open. Make sure you only use the APU/GTC air as this could shear the starter off 70psi from the engines. If it is still slow to start, it may be a sheared/jammed bleed air valve at the horsecollar.

Good hunting.

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About 35 years ago I had a start problem as you discribed. The speed sensitave valve had an internal failure and at approximately 40% RPM acceleration stagnated and TIT rose rapidly. We went through the procedures in the maint manual and it started with checking the acceleration bleed valves to see if they are open, which they were. Then it pointed to fuel components, but same as you, I did not have a high fuel flow for RPM. Disconnected the line to the acceleration bleed valves at the inline filter and started the engine, everything was normal for start. Replaced speed sensitive valve and engine start was back to normal.

There was no wind down associated with my problem.

Vic

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Swap a SSV with another engine... as for the initial "wind down" any other info moving the throttle when it happened or static?

I do second the idea of disconnecting the line to the acceleration bleed valves at the inline filter (cap it) and (try to start) or make sure all of your Acc bleed valves are open then try to start...

If it starts you will need to replace or bypass the SSV

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Glad you guys worked it out. If the engine has been sitting for a while, I suppose corrosion within the valve could have caused this defect, and it might have worked itself out after operating a few times. Be careful though. Without a solid fix, what happens once could likely happen again.

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