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Home > Flying on the Boeing 777 > Could the FO of the Boeing 777 crash have extended his glide?
Could the FO of the Boeing 777 crash have extended his glide?
Flying - Flying on the Boeing 777
Tuesday, 22 April 2008 11:30
Hi Capt Lim,

Can you advise as to what the First Officer of the Boeing 777 which crashed at Heathrow would have done to extend the plane's flight in an effort to reach the runway? This plane was very low, if descending from a cruising height without power, how would the pilot maximize the glide distance?

Is it true the Boeing 747 has the best glider characteristics for a commercial jet?

In a recent flight I got the impression that the entire landing was one long glide. Are pilots encouraged to "glide in" to save fuel?

I live local to a relatively quiet airport and through casual observation I suspect that the cheaper budget airlines, when having to do a 180 degree turn on approach, bank steeply and join the glide path at a very short distance from the runway. Again, is this to save fuel?

Regards,

John

Hi John,

At the 600 feet point where the Boeing 777 engines failed to respond for further thrust, the plane was at the landing configuration - meaning that landing gears and full flaps (30 degrees) were selected down. At that low altitude, there was no way that the gliding distance could be extended. Planes don't glide with full flaps as this setting creates an awful lot of drag and reduces the gliding distance. 

The only logical response at that moment, in order to maintain an adequate margin on the stalling speed so late in the approach, would be to dive at the perimeter and then convert that speed over the fence to reduced the sink rate by flaring a little (I believe it was erroneously reported that the pilot raised the flaps at that point). In fact, this maneuver actually reduces the gliding distance - hence landing short or else the aircraft would have stalled and dropped off the sky with even more disastrous consequences!

If descending from the cruise, the pilot can maximize his gliding range without power by flying at a best gliding speed (minimum lift/drag speed of about 250 knots). Say, at 35,000 feet, the plane can glide (clean without any flaps) for about 85 to 105 miles depending on the wind.

However, I am puzzled that the AAIB Report states that the autopilot disengaged at 175 feet. That meant the Boeing 777 was flown all the way by the autopilot and not manually by the pilot until at that point! Whatever it is, there was not much the First Officer could do besides desperately pushing the thrust levers forward to get more power. As it turned out, there were no additional power response and he only had to ensure that the wings were level before the impact as the directional control was more or less maintained by the autopilot up until 175 feet!

I cannot say with any great certainty that the Boeing 747 is a better glider (see the video ‘All Engines Out' below) of all the commercial jets. I would believe that a Boeing 777 would perform better as a glider (with all engines out) because it has only two engines and is more streamlined with a cleaner body.

It is not true that jet planes land like a glider (all engines out) to save fuel. In reality, all jet planes approach and land with at least some idle power (between about 20 to 55 % power).

Watch the interesting video on the Boeing 747 that lost all its engines and some facts about its gliding performance below...

Boeing 747 - All Engines Out
(You can see the full story here)

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Flaps
Hi John,

Actually the change in flaps from 30 to 25 performed by Captain Peter Burkill gave the aircraft sufficient lift to clear the perimeter fence and prevent what could've been a dreadful disaster.

Pick up his book and have a read - alternatively it is in the accident report.

RE gliding... the A330 has set the record for the longest glide without engine power (incident with fuel leak over the Atlantic). It also has a very clean airframe which is why you will notice when flying aboard one of these aircraft, the pilots may begin their descent up to 200mi before the destination.

Jack.
Jack Allison , 02 Aug, 2010
...
hi jack,
actually if you've flown a plane before you'd know that when you change from flaps 30 to flaps 25 the plane will initially sink before you would benefit from the extra drag and glide more from the improved lift/drag ratio. if captain peter changed the flaps at 1000 feet he would have glided further but by doing it just before impact he made matters worse.

yea i would believe that the airbus 330 is one of the best glider but the reason being why the pilots descend at 200 miles before the destination is because the fmgc calculates the descend with a little bit of thrust and not idle thrust. it assumes that anti ice will be used. i believe the boeing 777 would glide as well as an airbus 330

Caesar
Caesar , 23 Sep, 2011

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