Qantas B744 at San Francisco on Oct 6th 2016, bird strike

Last Update: June 29, 2017 / 16:37:09 GMT/Zulu time

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Photo of Qantas VH-OEH, Boeing 747-400 — Qantas VH-OEH, Boeing 747-400 (Photo credit: Simon_sees / Flickr / License: CC by)

Incident Facts

Date of incident
Oct 6, 2016

Classification
Incident

Cause
Bird strike

Airline
Qantas

Flight number
QF-74

Departure
San Francisco, United States

Destination
Sydney, Australia

Aircraft Registration
VH-OEH

Aircraft Type
Boeing 747-400

ICAO Type Designator
B744

A Qantas Boeing 747-400, registration VH-OEH performing flight QF-74 from San Francisco,CA (USA) to Sydney,NS (Australia), was climbing out of San Francisco's runway 28L when the crew heard abnormal noise and sensed unusual vibrations of the aircraft. The crew consulted with maintenance and performed troubleshooting. In the absence of any abnormal indications the crew decided to continue the flight to Sydney, where the aircraft landed safely about 14 hours after departure.

On Oct 14th 2016 the ATSB reported that a post flight inspection revealed a bird strike to a landing gear door strut and the door seal. The occurrence was rated an incident and is being investigated by the ATSB.

On Jun 29th 2017 the ATSB released their final report concluding:

Contributing factors

- During departure from San Francisco International airport, and unbeknown to the flight crew, one of the main landing gear door struts sustained impact damage from a birdstrike that resulted in the associated landing gear door not closing.

Other findings

- The noise and vibration experienced in the cabin was due to turbulent airflow associated with the un-closed landing gear door.

- The absence of cockpit indications and/or associated procedures to manage the observed vibration meant that the flight crew were required to use their professional judgement to assess its impact on the flight. The crew utilised available crew resources and maintenance expertise to troubleshoot and assess that the flight could safely continue to the destination airport.

The ATSB reported that soon after uneventful night departure from San Francisco the flight attendant located near door L3 contacted the cabin services manager (CSM) reporting vibrations and unusual noise in their area. Following the interphone call the CSM noticed increased noise and vibrations, too. In the meantime a training captain located in the cockpit noticed the increased noise and vibrations too, the captain under supervision was new to the aircraft and did not notice the unuusal noise and vibrations.

At the top of climb the fasten seat belt signs were turned off, the CSM contacted the flight deck to report the unusual noise and vibrations. All indications were normal, the second officer was sent to investigate the cause of the noise and vibrations. The first officer checked several sections of the cabin and determined that the noise was loudest near door L3. The CSM later recalled the second officer suspected a landing gear door seal. The second officer returned to the cockpit and briefed the other flight crew. Consultation with maintenance reaffirmed the suspicion of a landing gear door seal or wing to body seal as they are located near door L3. Together with maintenance the flight crew made several attempts to identify the source of the noise including isolating the air conditioning packs, air recirculation fans, re-selection of the landing gear lever to the UP position and checking toilets for vacuum leaks, however, the troubleshooting was unable to identify the source of the vibrations and noise. As the aircraft performed normally otherwise the flight crew decided to continue the flight.

The CMS later reported that the noise and vibrations persisted until the landing gear was extended for landing. The CMS also noted that no passenger commented on the noise or vibration.

The ATSB wrote: "After landing, ground engineers inspected the aircraft and immediately identified a protruding landing gear seal and initially thought this was the source of the vibration. On closer examination they observed that a rod, which normally attaches a small outboard landing gear door to the body landing gear shock strut, was sheared at the door attachment point as a result of a birdstrike."

The ATSB analysed:

Due to the physical size of the aircraft and the night departure, the birdstrike was not detected by the flight crew or ground personnel. Given the vibration was first noticed following retraction of the landing gear, it could be argued that the vibration was therefore directly related to the landing gear. However, all indications were that the landing gear had retracted normally. In addition, as there is significant additional noise and vibration while the landing gear is extended, it is equally plausible that this noise may have been masking something unrelated to the landing gear.

While the training captain was aware of some additional noise during the climb, all flight deck indications were normal including those for the landing gear. Due to sterile cockpit procedures, that limited other than emergency communications during critical phases of flight, the first indication that there was something abnormal was when the cabin services manager contacted the flight deck.

Once the nature and location of the vibration had been established, the flight crew proceeded to make use of all available resources to try and identify the source of the vibration and its implication for the continuation of the flight. In consultation with both maintenance operational control and cabin crew, the crew systematically isolated systems capable of generating the vibration. While they were unable to identify the source of the vibration, the flight crew established that it was constant and that the aircraft was otherwise performing normally. In the absence of any abnormal flight deck indications or relevant checklist, the decision to continue the flight was therefore at the discretion of the flight crew based on their professional judgement.

The landing gear system on the Boeing 747 uses a combination of hydraulics and attach rods to extend/retract both the landing gear and the associated doors. Proximity switch sensors located on both the landing gear and the hydraulically operated doors provide the flight crew with indications of both normal and abnormal operation. Small doors that are attached by rods directly to the landing gear, do not have proximity sensors as they normally open and close with the landing gear.

The discovery of the sheared attach rod, evidence of a birdstrike, and the reported in-flight vibration, is consistent with the aircraft having sustained a birdstrike during the departure and while the landing gear was extended. Due to the sheared attach rod, the associated landing gear door would not have closed resulting in residual turbulence and vibration being generated in the area of door L3. The lack of an associated proximity sensor meant that the flight crew were unaware that the door was not closed.