Re: ETOPS Question

Date:         03 Oct 97 01:18:34 
From:         jf mezei <"[non-spam]jfmezei"@videotron.ca>
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Eric Thomas wrote:
> >> Now, if the remaining engine fails, is it not rather pointless to
> >> require the true backup electrical systems (battery and prop-turbine) to
> >> operate for 180 minutes ?
> >
> > Yes, but you want your critical systems to continue operating so you can
> > control the plane on the way down (like Air Canada's Gimli Glider).

When flying at 42k feet which seems about the ceiling for commercial
passenger aircraft (except for Concorde), how long (max) would it take
for an engine-less plane to drop back to sea level an become a boat ?

In other words, how long would the backup electrical and hydraulic system
really be needed for in the worse case scenario with a lightly loaded
plane ? Are we talking 10 minutes, 30 minutes, an hour before the plane
gets to sea level ?

If that time were to be lets say 10 minutes, why would 180 minute ETOPS
certification require such truly backup system (when both engines fail)
to operate for 180 minutes ?