The last phase of recurrent simulator training for Cruise Relief First Officers (CRFO) included a two engine go-around after a slats drive failure. The outcome was usually surprising. For no apparent reason the AP/FD pitches to less than 10° (instead of the usual 15°) and accelerates well through the flap limit speed. The PF is required to disconnect and pitch manually above the flight director toward the standard 15 degrees to recover speed control.
Practices & Techniques: 5.34 Slats Drive Go-Around
A slats drive go-around has been shown in the simulator to have unusual flight characteristics. Boeing have confirmed that the simulator is following the same control law as the aircraft, and as such crew should expect the aircraft to behave the same way.
Essentially during a go around after a slats drive failure, the AFDS increases pitch rate slowly to a target of about 8-10° while airspeed continues to accelerate through the flap limit speed. The solution is to either disconnect and fly manually, or potentially a reversion to FLCH will restore correct AFDS speed/pitch behaviour.
An engine out slats drive go-around has the same pitch problem, although the result is less marked owing to reduced performance. Note that the use of FLCH to recover will reduce the thrust limit setting to the CLB/CON limit prematurely, and may compromise go around acceleration/performance.
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