Re: Slower aircrafts ?

Date:         28 Jun 98 18:47:37 
From:         k_ish <kenish@ix.netcom.com>
Organization: ICGNetcom
References:   1
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Frank Muenker wrote:
> I was recently on a Delta B767-ER (-200 I think) flight from Frankfurt to
> Cincinatti and the flight time was almost 10 hours. I could see on the
> monitors that the average cruise speed was only about 480 mph which is
> fairly slow compared to the 550 - 570 it could go. Also on 2 other
> inner-European flights ( about 4.5 hrs) with a B737 and a B757 cruise speed
> was way below 500 mph. I can recall that about 5 years ago cruise speed was
> always 520-570, at least on flights longer than 1 hr.
> I assume it has to do with fuel consumption, but does anybody know if the
> fuel performance is significantly better at lower speeds and if so why did
> they just start *now* to do that ? All aircrafts I was on looked like the
> newest models. Is it that  the latest models have a different curve of fuel
> performance ?

The monitors (more accurately the PFIS, or Passenger Flight Information System)
shows groundspeed, not airspeed.  Westbound there was probably a headwind.
Trans-Pacific it's not uncommon to see below 450 westbound and above 700
eastbound.

Ken Ishiguro