View Full Version : Jet engines on the ground

15th May 2004, 22:33
Noticed an engine (CF6 I think) on an A300 today, apparently 'free-wheeling'. The aircraft flys at night (freighter).

Would this have been down to the breeze flowing through the engine, or is there some mechanism to allow the engine to spin gently while at rest?

square leg
15th May 2004, 22:44
It would be down to the breeze. They call it windmilling. Be careful not to get dizzy while watching it (if it has a spiral on it's cone):D

Flight Detent
17th May 2004, 04:08
Hi guys,

Yeah, windmilling is very common for all big high-bypass engines whilst shut-down on the ground (and, come to think of it, inflt too!).
Anyway, no prolems except for engine start in windy conditions when the wind is from the rear quarter. Sometimes, the backwards windmilling fan will be very slow to start turning forwards, and can cause abnormally high EGT start peaks, sometimes TOO high, and cause precautionary aborted starts.

I remember that when engine starting the RAAF Mirages (a few years ago now!), if the wind was from the rear and windmilling the engine the wrong way, we couldn't start at all. So they incorporated small 'blowers' on ground crew backpacks to blow air down the intake at initiation of start, to have the engine turning the correct way, and it started OK.

Getting back to the big engines, if you were close enough to hear, the fan blades are also moving in their mounts with each rotation, causing a quite loud 'clanking' noise, also quite normal to those that are around airplanes all the time, but a concern for remotely loaded pax, from the bus, when they walk past Nos.1&2 engines and up the forward steps, I hear the FAs calm their concerns several times each time we are in that situation.


17th May 2004, 08:05
Windmilling of TurboFan Engines can be a major problem.
CFM56-3 motor AMM says that if it has windmilled for more than 6 hours the engine must be replaced.
During the windmilling action the lubrication pumps with-in the lube unit turn into scavenge pumps removing oil from the oil tank and placing it into the engine sumps damaging the ail-oil seals.This is why some airlines fit engine fan straps to engines in ports where engineers do not provide 24 hour coverage.
From memory the CF6 and the CFM56-5 motors had more tolerance (think it was @8hrs)

Capt Claret
17th May 2004, 22:58
Flight Detent

I've heard of a flight being signifficantly delayed checking for a suspected bomb, after a new to jets F/O alerted the skipper to a ticking sound.

Possibly an urban myth, possibly true. :8