Thomson B763 at Bristol on Oct 3rd 2010, hard landing

Last Update: May 10, 2012 / 14:34:36 GMT/Zulu time

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Photo of Thomson Airways N852UA, Boeing 767-300 — Thomson Airways N852UA, Boeing 767-300 (Photo credit: DearEdward / Flickr / License: CC by)

Incident Facts

Date of incident
Oct 3, 2010

Cause
Hard landing

Airline
Thomson Airways

Aircraft Registration
N852UA

Aircraft Type
Boeing 767-300

ICAO Type Designator
B763

The AAIB released their bulletin concluding the probable cause of the accident was:

Damage to the fuselage occurred as a result of rapid de‑rotation of the aircraft following a hard landing on the main landing gear. The runway profile, nuisance GPWS alerts and the meteorological conditions may have influenced the landing.

The aircraft was on approach to Bristol with the first officer being pilot flying. Weather conditions were reported as visibility of 1400 meters/4600 feet, winds from 100 degrees at 10 knots, scattered cloud ceiling 100 feet AGL, broken cloud ceiling 400 feet AGL and runway 09 in use with RVR above 1500 meters/5000 feet. ATIS reported water patches on the runway. Surprised by the poor weather conditions in contradiction to terminal area forecasts received prior to the flight the captain (49, ATPL, 14,433 hours total, 1,355 hours on type) decided to fly the landing himself and took control of the aircraft. The first officer reviewed landing performance due to the patches of water report and found the runway sufficient for the landing. The computed Vref was 133 KIAS, the captain decided to use a Vapp of 139 KIAS for flaps 30.

Upon checking in tower reported the winds from 120 degrees at 12 knots, visibility 3000 meters/10,000 feet in moderate rain, few clouds at 200 feet AGL and broken cloud at 1100 feet AGL, the runway surface was wet all along and there were no water patches.

The captain recollected the FMC computed a cross wind component of 52 knots requiring a considerable drift angle. The surface wind report prompted the commander to expect a change from crosswind to head wind with a considerable ballooning effect and instructed the first officer to watch the FMC wind display and report any substantial changes.

The captain became visual with the runway while descending through 400 feet AGL, the first officer was unable to see the runway that was obstructed by the windshield pillar as result of the drift angle. The captain disconnected autopilot and autothrust and continued the approach manually. When crossing 200 feet AGL the FMC indicated winds from 138 degrees at 25 knots, the airspeed was 141 KIAS at that time. Below 200 feet AGL the EGPWS issued two or three glideslope warnings, the captain confirmed the PAPIs were showing two white two red indications and continued the landing. Descending through 120 feet AGL engine EPR increased slightly and the airspeed increased from 138 KIAS to 146 KIAS, at that time the attitude increased from 2.5 to 4 degrees nose up, followed by reduction of engine thrust and pitch down control input. Descending throgh 35 feet the attitude was 1 degree nose up, airspeed was 142 KIAS, the aircraft descended at 600 feet per minute, the FMC computed the wind from 116 degrees at 20 knots. During the next three seconds the attitude progressively increased to 3.5 degrees nose up, the rate of descent however only gradually reduced.

The aircraft touched down at 141 KIAS in what the commander perceived as a normal nose up attitude, the touch down was unusually hard however, the flight data recorder registered a vertical acceleration of +2.05G. Both crew reported they were thrown forward at touch down resulting in the commander inadvertently moving the control column forward to a nose down attitude and the aircraft rapidly de-rotated, the flight data recorder registered a longitudinal acceleration of -0.27G at touch down followed by a nose down control column movement less than 0.5 seconds later, the spoilers began to extend automatically. The aircraft reached a nose down attitude, the main gear became "light", and the nose gear touched down at a pitch angle of -1 degrees (nose down), another vertical acceleration of +2.05G was recorded upon nose gear touchdown. The aircraft subsequently oscillated between -0.5 and +3.0 degrees of pitch angle indicating the nose gear bounced until the aircraft's gear settled firmly on the runway. Seven seconds after main gear touch down the thrust reversers were applied. The FDR suggested there had been no braking during the initial stages of touch down. The aircraft rolled out without further incident and taxied to the apron. The captain made a tech log entry regarding a suspected hard landing and reported the suspected hard landing to maintenance. Unaware of the damage the aircraft had received the crew left the aircraft.

The AAIB reported that the cockpit voice recorder was not available for the investigation, the circuit breaker had not been tripped after landing or arrival at the gate despite the crew suspecting a hard landing and the recordings of the landings had already been overwritten when the CVR was finally stopped.

A first examination of the aircraft revealed significant damage to the crown skins between frames STA 610 and STA 632 and stringers 14L and 14R. All stringers in that area were cracked, bent or deformed, the skin was creased and wrinkled. 5 frame segments were twisted and deformed, frame STA632 was cracked.

The AAIB reported the met services determined in their analysis that there were a number of convective cells along the approach path that would have produced vertical motion of air, which likely caused some turbulence on the approach to Bristol. The "relatively rapid" changes of wind direction and speed with height suggested a potential for significant windshear induced turbulence concluding "conditions were suitable (or very close to) for significant wind shear."

The airport reported that the profile of the runway was not in line with CAP standards and may have presented an unusual visual perspective on final approach. In addition, the glideslope was not useable below 200 feet AGL and therefore may produce nuisance GPWS glideslope alerts while properly tracking the PAPIs. Bristol's flight monitoring programme identified six of 709 landings on runway 09 as hard, in the same time frame only one hard landing had occurred on runway 27.

The aircraft manufacturer analysed that a longitudinal acceleration of -0.27G at touch down was normal and not unique to the B767, there was no evidence that any crew had inadvertently moved the control column as result of that longitudinal deceleration. The deceleration pulse is the result of the main wheels spin up. The manufacturer concluded the deceleration was "insufficient magnitude and duration to cause a pilot to be thrown forward with sufficient force so that the control column would be inadvertently held in a nose down position."

The aircraft had already suffered a similiar accident in 2000 while still registered as S7-RGV resulting in wrinkles of the crown skin. The damage had been repaired by Boeing.

The AAIB analysed: "Despite the turbulence, the approach itself was stable and within normal parameters. The absence of a usable glideslope indication below 200 ft aal, the EGPWS Â‘glideslopeÂ’ alerts, and the absence of an automatic height call-out at 30 ft aal were unhelpful. The profile of the runway deprived the commander of sight of the full length of the runway as the aircraft approached the flare, and probably contributed to the high rate of hard landings (the flight crew training manual emphasised the importance of shifting the visual sighting point to the end of the runway)."

There was no evidence to suggest that the previous hard landing and repair had any bearing into the accident at Bristol.

The AAIB further analysed that had the crew not only applied their shoulder harnesses, but also locked the inertia reels of the shoulder harnesses, the crew would not have been thrown forward to the degrees they did, and the inadvertent movement of the control column may have been avoided or lessened.

Boeing had released training materials in response to several hard landings, the materials however were released outside the usual ways of distribution and thus were not known to the airline and the crews.