B752, San Jose Costa Rica, 2022
B752, San Jose Costa Rica, 2022
On 7 April 2022, a Boeing 757-200F returning to San Jose after a left side hydraulics failure and MAYDAY declaration suddenly veered off the right hand side of the landing runway there during deceleration and passage over uneven ground led to landing gear collapse and significant fuselage structural damage. This runway excursion immediately followed simultaneous advancement of both thrust levers after their prior asymmetric movement earlier in the landing roll and resulted in high left thrust concurrent with idle thrust on the right. With no airworthiness aspect identified, the excursion was attributed to unintended thrust lever selection by the crew.
Description
On 7 April 2022, a Boeing 757-200F (CC-BHB) being operated by DHL Aero Expresso a scheduled international cargo flight from San Jose to Guatemala City as DO7216 experienced a loss of the left hydraulic system during the climb and levelled off at around FL200. A MAYDAY was declared with the advice to ATC that it was intended to return to San Jose. Whilst flying a holding pattern, the corresponding Non Normal Procedure for the left hydraulic system failure was carried out and the return was the approved and flown in day VMC without further event until the aircraft suddenly veered off the landing runway onto uneven ground as it decelerated. This excursion resulted in the impact removal of the landing gear and significant airframe and engine damage but both pilots, the only occupants, were able to exit the aircraft uninjured.
The aircraft where it finally stopped. [Reproduced from the Official Report]
Investigation
An Accident Investigation was carried out by the Costa Rican Accident and Incident Unit Civil Aviation Technical Council (CETAC). The SSFDR, the 2 hour CVR and QAR were removed from the aircraft and all their data were successfully downloaded by the NTSB but as that on the QAR was the same as on the SSFDR, it was not further examined. Analysis of both sets of data was facilitated by the NTSB.
The 58 year-old PF Captain had a total of 16,381 hours flying experience including 6,233 hours on type. The 43 year-old First Officer had a total of 10,545 hours flying experience including 2,337 hours on type. Both pilots were Guatemalan nationals.
What Happened
With the Captain as PF, the flight took off from runway 07 at San Jose and initially followed the NANJO 33 SID with clearance to climb to 13,000 feet before being re-cleared to FL220. Following receipt of this re-clearance, an indication of low hydraulic fluid quantity was annunciated and this was then followed by an alert advising L HYDRAULIC PRESSURE LOW and the crew reported having noticed that the left and centre APs and the YD were no longer functioning. The climb was stopped at around FL 200 and a MAYDAY declared and acknowledged. ATC was requested to approve the flight holding at the PARZA waypoint to prepare for a return to San Jose and the corresponding QRH Non Normal Procedure was actioned.
The aircraft was descended to 18,000 feet and the right AP was engaged. The First Officer checked the landing performance and confirmed that the aircraft would be well below the applicable maximum landing weight (MLW) for a landing on runway 07 and a briefing for an ILS approach and an emergency landing was completed. It was noted that the VREF would be 130 KIAS and that the landing would be without nose wheel steering, autobrakes, left reverse thrust and automatic rudder deflection adjustment for airspeed with only limited spoiler deployment possible.
The return proceeded normally and with the flight established on the ILS, TWR issued a landing clearance, gave a spot wind 240°/10 knots and confirmed that RFFS vehicles were in position. A normal touchdown then followed two minutes later with directional control initially maintained using rudder, differential braking, right thrust reverser and manual deployment of the speed brakes. However, as the aircraft approached taxiway Delta, at a ground speed of approximately 60 knots it began an uncontrolled turn to the right which resulted in it exiting the runway to the south. This right turn continued until terrain impact broke off the main gear legs and the aircraft came to an abrupt stop still south of the runway with the tail section almost completely separated from the rest of the fuselage and the aircraft nose on taxiway ‘K’. Both engines and the APU were shut down and both fire handles were pulled. There was no fire despite wing damage and the two pilots were able to leave the aircraft via a ladder provided by the RFFS.
A view of the ruptured rear fuselage. [Reproduced from the Official Report]
All structural damage to the aircraft was found to have been attributable to terrain impact forces during the runway excursion. Damage to the turbine blades of the left engine was found to have been caused by ingestion of terrain material when it was in ground contact following the main gear collapse whilst it was still running.
Why It Happened
- The hydraulic system fluid loss which prompted the MAYDAY turnback was found to have been caused by multiple fractures of wire strands, delamination/loss of material, fatigue and ductile separation with cracks and voids in individual cables in a section of the left hand MLG Downlock Actuator Retraction Hose cross section due to fatigue and tension in the material.
- The sudden runway excursion after the initially normal landing roll could be clearly seen from FDR data to have occurred when the (correct) cessation of right engine reverse as the ground speed reduced through about 60 KIAS was accompanied by an inappropriate, sudden and rapid forward movement of the left engine thrust lever from at or about the idle position to 92% N1. An examination of all systems which might have caused this and their corresponding flight data failed to identify any malfunction which could have been responsible and the Investigation therefore tentatively attributed this action to an unappreciated ‘muscle memory’ input by the Captain. It was noted that during interview, neither pilot had understood what had initiated the sudden runway excursion.
Two Contributory Factors to the Accident were formally identified as:
- Fatigue and stress on individual cables in the hose cross section of the flexible hydraulic retraction downward lock actuator for the left main landing gear.
- The probable inadvertent synchronised (forward) movement of the right engine “Reverse Thrust Lever” and the left engine “Thrust Lever” as a consequence of muscle memory.
A total of 6 Safety Recommendations were made as a result of the Investigation as follows:
- that the Federal Aviation Administration (FAA) as State of Manufacturer and issuer of the aircraft Type Certificate publish, as soon as possible, an Airworthiness Directive (AD) in which compliance with SB 757-29-0056 is made mandatory. [RSO-01-CR-ACC-CO-002-2022]
- that Boeing Commercial Airplanes issue, as soon as possible, an additional communication to 757 operators in which this event is made known and advises them to consider replacing the presently programmed (soft Time) replacement sets of flexible hydraulic main landing gear hoses with replacement at intervals dependent on the operating environment of each operator and their experience according to their component reliability programmes which would reinforce the existing best practice recommendation in Boeing SL 757-SL-29-053 dated 22 August 2022. Boeing should also emphasise the recommendation for compliance with the SB 757-29-0056 dated 8 February 2001 which covers topics linking improvements to the 757 main landing gear descending lock actuator retraction hoses. [RSO-02-CR-ACC-CO-002-2022]
- that DHL de Guatemala S.A. implement, as soon as possible and as a proactive mitigation measure, a frequency of change of flexible hydraulic landing gear hoses greater than that required in the current Boeing Maintenance Programme. [RSO-03-CR-ACC-CO-002-2022]
- that DHL de Guatemala S.A. reinforce, as soon as possible, the training of maintenance teams on hose installation procedures for flexible hydraulics, with the aim of preventing strangulation of these and minimise stress due to fatigue. [RSO-04-CR-ACC-CO-002-2022]
- that DHL de Guatemala S.A. review, as soon as possible and reinforce in pilot training the Non Normal Procedure response to HYDRAULIC QUANTITY and HYDRAULIC SYSTEM PRESSURE considering the lessons learned in this Investigation, giving special emphasis to Crew Resource Management (CRM). [RSO-05-CR-ACC-CO-002-2022]
- that the Costa Rican Civil Aviation Technical Council (CETAC) order an evaluation of ground traffic movement at San Jose Airport as soon as possible so as to correct or mitigate any possible deficiency in operational safety such as the one identified when this runway excursion resulted in the blocking of taxiway ‘K’ and thereby impeded the transit of RFFS vehicles from their base towards the active runway. [RSO-06-CR-ACC-CO-002-2022]
The Final Report was completed on 7 September 2023, formally approved by the CETAC on 12 September and published in Spanish only on 22 September 2023.
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