B734, East Midlands UK, 2023
B734, East Midlands UK, 2023
Summary
On 1 December 2023, a Boeing 737-400 crew about to depart East Midlands on a night cargo flight set up the departure based on an incorrect loadsheet. As a result, the actual takeoff weight was 10 tonnes heavier than anticipated. Although no handling abnormality was detected, a ‘bump’ was heard during rotation and suspected to be either load shift or a tail strike. After an inspection eliminated load shift, it was decided to assume a tail strike and complete the forty five minute flight at a reduced altitude. This occurred without further event and a tail strike was subsequently confirmed.
Event Details
When
01/12/2023
Day/Night
Night
Flight Conditions
On Ground - Normal Visibility
Flight Details
Aircraft
Operator
Flight Origin
Intended Destination
Take-off Commenced
Yes
Flight Airborne
Yes
Flight Completed
Yes
Phase of Flight
Take Off
Location - Airport
Airport
General
Tag(s)
Flight Crew Training,
Use of Erroneous Performance Data
HF
Tag(s)
Pre Flight Data Input Error
GND
Tag(s)
Cargo Aircraft Loading
LOC
Tag(s)
Aircraft Loading,
Take off Trim Setting
Outcome
Damage or injury
Yes
Aircraft damage
Minor
Non-aircraft damage
No
Non-occupant Casualties
No
Off Airport Landing
No
Ditching
No
Causal Factor Group(s)
Group(s)
Aircraft Operation
Safety Recommendation(s)
Group(s)
None Made
Investigation Type
Type
Independent
Description
On 1 December 2023, a Boeing 737-400 (G-JMCV) being operated by West Atlantic on a scheduled cargo flight from East Midlands to Aberdeen as NPT2876 and being used for line training unintentionally departed with the aircraft 10 tonnes heavier than the weight used to set up the takeoff. No unusual handling was detected during takeoff but an abnormal noise led the crew to suspect either load shift or a tail strike and having eliminated load shift, concluded a tail strike must have occurred which was then confirmed by damage observed after arrival in Aberdeen.
Investigation
A Serious Incident Investigation into the event was carried by the UK Air Accident Investigation Branch (AAIB). Relevant recorded data from the FDR was not available but corresponding QAR data was obtained and analysed by Boeing. It was noted that the 44 year-old Training Captain in command had a total of 7,649 hours flying experience which included 2,720 hours on type but the First Officer’s experience was not recorded.
What Happened
The two pilots arrived at the aircraft at 0430 and the Captain observed that it required de-icing and called for this. It was subsequently carried out by two separate vehicles whose operators provided separate receipts to the Captain, both of which had errors which the Captain asked the assigned Dispatcher to get corrected.
The Dispatcher later returned and gave the Captain a number of forms relevant to the flight including but not limited to the corrected de-icing forms, NOTOCs (Notification to Captain) relating to the dangerous goods loaded and the load and trim sheet for the flight. Whilst loading was being completed, the Captain checked what he believed was the correct loadsheet and having confirmed that it was, signed it. The crew then used their individual Boeing OPTs (Onboard Performance Tool) to calculate the takeoff performance data using the weight and balance information contained on the loadsheet he had checked.
Before setting thrust for the takeoff from runway 27, the Captain, who was acting as PF, performed an engine run up check due to the prevailing low air temperature. He reported that although he had considered the rotation to have been normal, both pilots had recognised a “small bump” as it occurred. After completing the After Takeoff checks, he reported that they had discussed the possibility that the bump might have indicated either a tail strike or a load shift but in the absence of any abnormal indications or aircraft handling, it was decided to continue to the planned cruise altitude of FL240.
Aware that the OM Part B included guidance in the event of a load shift which stated that “should a load come loose, there is a serious risk to the aircraft”, on reaching FL240, the Captain asked the First Officer to visually check the cargo hold in order to resolve any concerns regarding unsecured cargo. Since he was aware that the middle bay ‘B’ of the three-bay cabin was empty, he was concerned that cargo from Bay A could have moved aft. However, the First Officer could only see the cargo in Bay A and reported that it appeared to be secure. The NNC for a possible tail strike was consulted and it was decided that in the absence of any other explanation for the ‘bump’ at takeoff, it should be actioned. Given the First Officer’s inexperience, the Captain decided to carry out the descent to FL 090 before depressurising which was then performed. The remainder of the flight was uneventful and landing at Aberdeen occurred after 55 minutes airborne. Once the aircraft had been parked and shut down, the Captain carried out an external inspection and found damage to the tail skid and a drainage mast. The crew reviewed their paperwork and discovered that the loadsheet the Captain had signed was not the one they had used for OPT input.
Why It Happened
It was found that although not appreciated at the time, the Dispatcher had inadvertently included two different loadsheets in the sheaf of papers which they had handed to the Captain prior to departure, one of which was from “a previous flight”. The Captain had inadvertently used the wrong loadsheet as the source of data for input to the pilot’s OPTs which had therefore output incorrect takeoff performance data. Although this did not affect the flap setting which was 5° in either case, it led to the use of a takeoff weight of 43 tonnes instead of the actual figure of 53 tonnes. This in turn produced V1/VR/V2 speeds of 115/124/131 knots instead of 128/139/147 knots and an N1 of only at 81.9% instead of the correct 86.8%. The stabiliser trim setting output used for takeoff also gave a slightly more nose-up trim than the correct figures would have done.
QAR data showed that rotation had begun at approximately the speed set by the crew with the aircraft’s attitude starting to increase after two seconds with the instantaneous pitch rate peaking at 5° per second just prior to lift off. However lift off did not occur until a recorded 137 KCAS - 13 knots above the bugged VR of 124 knots. At this time, the pitch attitude was recorded as 12.3° which exceeded the pitch attitude for a tail strike of 11.4°. It was noted that the aircraft had not lifted off at the point in the rotation anticipated by the Captain but only after (and because) he had continued the rotation as the speed increased. It was also noted that as the stabiliser trim setting used was more nose-up than for the correct takeoff weight, pitch control forces would have been lighter than anticipated by the Captain and may have contributed to the pitch rate peaking at 5°/second just before the tail struck the ground.
It was noted that the FCTM stated that a takeoff with flap 5 set should see lift off occur at 9.1° pitch attitude with a minimum tail clearance of 23 inches and the tail strike attitude being 11.4° with the main wheels on the ground. The FCTM lists five factors liable to increase the tail strike rise, one of which is a mis-trimmed stabiliser which it says “usually results from the use of erroneous takeoff data”. It also states that any of following can indicate a tail strike:
- a noticeable bump or jolt
- a scraping noise from the tail of the airplane
- pitch rate stopping momentarily
and advises that after any fuselage contact is suspected or confirmed, the tail strike NNC should be accomplished “without delay”.
The Conclusion of the Investigation was documented as follows:
The crew used incorrect loading figures to calculate the aircraft performance at departure. The aircraft was approximately 10 tonnes heavier than anticipated and the PF therefore commenced the takeoff rotation 15 knots too slow. Due to the lower speed the wing did not develop sufficient lift for the aircraft to takeoff as expected and the tail struck the ground.
The Final Report of the Investigation was published on 8 August 2024. No Safety Recommendations were made.
