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In the El Al 1862 crash, the flight crew lost control of their 747 in what basically amounts to an aggravated Vmca roll during approach after two engines detached from the aircraft, causing the loss of two hydraulic systems and damage to flight control surfaces on the right wing.

What was the actual Vmca of the aircraft in that damaged configuration though? Further, if they had not been focused on trying to get down to a normal configuration Vref and instead sped back up as soon as they started nearing full control deflection, thus increasing their control authority, could they have gone around and then reconfigured partially for what would be an increased Vref, then landed the aircraft at that increased speed? Schiphol has no shortage of runway, after all...

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    $\begingroup$ You can't expect a pilot to be able to handle an aircraft with a completely altered dynamics, flight, and control envelopes. $\endgroup$
    – user7241
    Commented Dec 24, 2017 at 11:09
  • $\begingroup$ @jjack Not in general, you‘re right. But there are some examples where crew succeeded in doing just that, at least partially. The most successful example would be the 2003 Baghdad incident DHL crew who landed their damaged Airbus A300 without any conventional flight controls using only engine thrust modulation. $\endgroup$
    – Cpt Reynolds
    Commented Dec 24, 2017 at 20:12
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    $\begingroup$ @jjack -- the key to dealing with an aircraft that's had its envelope altered by damage is to figure out what the plane can and can't do while still at a safe altitude (i.e. a controllability check). $\endgroup$
    – UnrecognizedFallingObject
    Commented Dec 24, 2017 at 20:16
  • $\begingroup$ @UnrecognizedFallingObject The length of the checklist is well suited for a safe altitude... $\endgroup$
    – user7241
    Commented Dec 24, 2017 at 20:45
  • $\begingroup$ @CptReynolds Is there a statistic giving the number of successful recoveries against the number of losses? It would have to exclude the impossible cases. $\endgroup$
    – user7241
    Commented Dec 24, 2017 at 20:50

1 Answer 1

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The accident report says

2.4.2 Performance

An energy analysis was performed based upon altitude and airspeed data from the DFDR. It should be realised that this method does not allow extrapolation of performance capabilities in other conditions then those encountered during this flight. Based on this analysis the following conclusions can be made:

  • Marginal level flight capability was available at 270 knots and go around power with a limited manoeuvring capability;
  • At MCT thrust and 270 knots IAS there was no level flight capability;
  • Performance degraded below about 260 knots at increased angles of attack. Deceleration to 256 knots resulted in a considerable sink rate.

(my emphasis)

My interpretation is that it is not appropriate to define a Vref for a 747 in that configuration.

Glossary

Vmca = Minimum Control (air) Velocity. Min speed that directional control can be maintained. Vmca2 for two engines (critical and inboard on same side) of a 4-engine aircraft.

Vref = Speed required as the landing runway threshold is crossed at a height of 50 feet in landing configuration.

MCT = Maximum Continuous Thrust. Thrust levels higher than this can only be maintained for a short time (e.g. minutes).

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  • $\begingroup$ It also means that basically, there isn’t any excess energy available at TO/GA power (takeoff/go-around), so that there is no real chance of accelerating once too slow, and also no chance of attempting a go-around if the approach fails. $\endgroup$
    – Cpt Reynolds
    Commented Dec 24, 2017 at 20:15
  • $\begingroup$ @CptReynolds Is the thrust rating setting (max TO, max Continuous, max Climb, and so on) selectable by the pilot or is it restricted to a certain part of the flight envelope by the avionics (or both)? $\endgroup$
    – user7241
    Commented Dec 24, 2017 at 21:08
  • $\begingroup$ @jjack On the aircraft I am familiar with (mainly Airbus and Boeing), it is selectable by crew. $\endgroup$
    – Cpt Reynolds
    Commented Dec 28, 2017 at 17:25
  • $\begingroup$ "Thrust levels higher than this can only be maintained for a short time (e.g. minutes) without risking damage to the engines" would be more accurate. $\endgroup$
    – Vikki
    Commented Oct 8, 2019 at 1:50

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