Report: Excessive nose gear derotation caused serious damage to Boeing 757, Azores, Portugal
The crew anticipated and prepared an ILS approach to runway 30, however, on the descent to Ponta Delgada, the flight was cleared for RNAV (GNSS) Z approach for runway 12.
Due to the aircraft estimated landing weight of 196000lb and the maximum authorized landing weight (MLW) of 198000lb, the crew reviewed the landing parameters calculating the reference speed (Vref) with 133kt, the landing distances and opting for the brake 4 on the aircraft automatic brake system, based on the company guidance for the destination airport. The reported wind to the crew was 050° with 16kt, variable between 020° and 080°, with a local temperature of 21°C.
During the approach, around 1500ft, the co-pilot who assumed the position of the pilot flying (PF), uncoupled the autopilot and followed the operator standard operational procedures SOPs.
On short final, some speed variations were felt with the respective corrections in the flight controls and engine power adjustments by the PF closely followed by the pilot in command (PIC) adding verbal inputs.
The initial touchdown was on the left main gear, followed by the right main gear, both contacts were considered normal. Right after that, the aircraft nose abruptly pitched down and the nose landing gear touched hard on the runway.
The aircraft was on the runway centreline and, after the hard touch of the nose landing gear felt and commented by the pilots, it decelerated rapidly. Right after that and still without realizing what had happened, at a speed of approximately 100kt, the pilot in command (Captain) took control of the aircraft.
The aircraft, after deceleration, reversed the direction of travel on the runway and headed for the assigned parking space, without anomalies by the crew.
During the post-flight walk-around, damage was observed on the lower front fuselage landing gear and on the upper central area in front of the wing. The aircraft suffered damage on the primary fuselage structure with deformed frames, stringers and skin, as well as permanent nose landing gear axle deformation.
The Portuguese accident investigation board GPIAAF classified the occurrence as a 'Serious Incident'. By ICAO definitions, rating the occurrence an 'Accident' would seem to be more appropriate as the aircraft sustained damage which "adversely affects the structural strength [..] of the aircraft" and required "major repair".
The aircraft in question was ferried to Atlanta on 19 September, then on to Jacksonville (VQQ) on 13 October. It re-entered service after repairs on December 1, 2019.
Probable cause: The excessive nose landing gear derotation rate, resulting in a hard landing with nose gear overload.
To this event would have contributed the following factors or their combination:
- the clearance for RNAV (GNSS) approach on runway 12 when the crew have prepared the ILS approach on runway 30;
- PF piloting technique with excessive corrections of attitude and thrust corrections, namely the excessive nose down elevator input after MLG touchdown;
- For the repeatedly PF corrections, may had contributed the lateral northeast crosswind effect during the landing (050° with 16kt variable between 020° and 080°);
- the aircraft's mass on landing contributed to the consequences on the inflicted damage to the primary structure.
The engines thrust reduction during the derotation movement, enhancing the excessive moment around the aircraft lateral axis cannot be excluded as a possible contribution factor. ■