View Full Version : Start valve manual opening

19th Jun 2023, 22:52
Hi ..
talking about cfm 56 engine start in case of start valve fail to open automatically , and have to open manually , if the technical personal doesn't closes the valve at 50% N2 ! What is the impact of this procedure on the ( starter / the valve )
Are there any chance to abort the starting sequence. .
need a technical answer with details. .
thanks in advance.

19th Jun 2023, 23:10
If you don't close the valve the starter motor will continue to run and probably experience a RUD!
There was a time that dispatch with a U/S start valve was prohibited due to the CFM56 windmilling too slowly to restart in flight without the starter. Is this still the case? It's been a while.

20th Jun 2023, 14:21
I'm not familiar with the engine, but most that I know the start valve is spring loaded closed and pulling the starter switch allows reverse flow of air, which returns to normal flow after start switch off? I stand to be corrected of course.

20th Jun 2023, 18:17
If the starter stays engaged once the engine is running, it will overspeed when the engine goes to power and will likely explode (it is shielded to prevent the shrapnel from causing critical damage to the rest of the engine, but it's still highly undesirable). This is a rare failure, but it has happened.

20th Jun 2023, 22:20
There's no big difference between start valve not closing automatically and the ground crew/engineer not closing it - in both cases you would have START VALVE OPEN indication on the upper DU, which would lead you to the related NNC, which essentially shuts off the bleed air supply on the affected side, and - if that isn't successful - shutting down the engine.

This all assumes that you've lost interphone contact with the person operating the start valve override, and you can't just tell them to close the valve.