PDA

View Full Version : Clunking sound on engine spooldown CRJ900

vgtvgt
18th Oct 2019, 08:25
Hi,

I'm an enthusiast and not a pilot, please excuse me if I'm talking nonsense. Couldn't find any information on this elsewhere.

Is it normal for CRJ900 engine to emit clunking sound when spooling down? If no, is this indicating something dangerous?

Two weeks ago I was on a Copenhagen-Wroclaw SAS flight (operated by CityJet I think) in a CRJ900. Wind in Wroclaw was very strong and the pilots didn't manage to land on two approaches and decided to go back to Copenhagen. As far as I know all other flights made a successful landing that day in Wroclaw. When back on the ground in Copenhagen after disembarking the aircraft I noticed that left engine was emitting loud clunking sound. This made me think if there was something wrong with it and if the captain made a decision to not to try again/wait based on some abnormal engine parameters.

Thank you,
Tadeusz.
Uplinker
19th Oct 2019, 08:14
This is a guess, but were you hearing the front fan blades clunking as they turned in the wind?

The front fan blades of modern jet engines are slightly “loose” in their sockets. When the engine is started, and the fan turns, centripetal force pulls the blades outwards and locks them into position.

When the engine has been shut down but the fan is lazily rotating, you can often hear the fan blades clunking as the fan turns. On some engines, such as the CFM 56, this can cause a real racket in a stiff breeze, and it sounds most unhealthy, but is absolutely fine.
Denti
19th Oct 2019, 14:49
When the engine has been shut down but the fan is lazily rotating, you can often hear the fan blades clunking as the fan turns. On some engines, such as the CFM 56, this can cause a real racket in a stiff breeze, and it sounds most unhealthy, but is absolutely fine.
On the older CFM56, the newer ones, like those on the 737NG do not clunk anymore. It is a slightly different construction, which is understandable as it has a lot less fan blades as well, I believe 17 instead of 36 blades on the fan of the CFM 56-7B compared to the CFM 56-5B, but i might be wrong.