Re: 757 engine (fan?) noise during freewheel

From:         tristar500@aol.com (TriStar500)
Organization: America Online, Inc. (1-800-827-6364)
Date:         28 Sep 95 03:52:44 
References:   1
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>Frequently when boarding a BA 757 (RR engines) by steps rather than
>through an air bridge I hear a distinct metallic clanking from the
>engine closest to me,

The sound you hear is the blades hitting each other! The fan blades ( on
any fan engine, not just those from RR) are not ridgidly attached to the
hub, they are allowed to move some. As the fan rotates the blade at the
top flops to the other side and hits the blade next to it.

Perfectly normal, in fact the problem comes when the blades don't clank.
This causes an imbalance in the fan and vibration.


>which is nearly always still freewheeling from the previous sector.

You said you were boarding when you heard the sound, so at least 15-20
minutes have passed since the engine was shutdown. I'd say it's wind
causing the fan to turn.