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| Date: | Wednesday 18 September 1996 |
| Time: | 10:29 |
| Type: |  Boeing 737-4Q8 |
| Owner/operator: | British Airways |
| Registration: | G-BSNW |
| MSN: | 25169/2237 |
| Year of manufacture: | 1992 |
| Engine model: | CFMI CFM56-3 |
| Fatalities: | Fatalities: 0 / Occupants: 123 |
| Other fatalities: | 0 |
| Aircraft damage: | None |
| Location: | Near Florence -
 Italy
|
| Phase: | En route |
| Nature: | Passenger - Scheduled |
| Departure airport: | London-Gatwick Airport (LGW/EGKK) |
| Athens-Ellinikon International Airport (ATH/LGAT) | |
| Investigating agency: | AAIB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The aircraft departed from London Gatwick for a scheduled flight to Athens with the first officer as
handling pilot. A fuel load of 13,200 kg had been selected by the commander and this resulted in full
wing tanks and 4,000 kg in the centre tank. In accordance with standard operating procedures, all
6 booster pumps (two in each of the three fuel tanks) were selected on prior to start. With these
switch positions, pressure differentials within the fuel system would mean that the center tank fuel
would be used before the fuel in the two wing tanks
The take off and climb were uneventful and the first officer engaged Autopilot 'B' as G-BSNW
climbed through FL 140. Towards the top of the climb, the commander noticed a small imbalance
of fuel; the left wing was indicating approximately 150 kg more than the right wing. He mentioned
this imbalance to the first officer and advised him of his intention to balance the fuel. By now, the
aircraft was level at FL 290 and the crew were advised by ATC that FL 290 would be the final
cruising level rather than the planned FL 330. At approximately 0912 hrs, the commander then
selected the left center booster pump to off; no other fuel switches were moved. His intention was
that the left wing tank would supply fuel to the left engine and the center tank would supply fuel to
the right engine, thereby balancing the fuel between the two wing tanks. The commander annotated
his SWORD (Flight-log) with "Fuel Bal" and drew an 'attention line' down the right side to a point
approximately 27 minutes later; the commander also made a mental note to check the balance after
five minutes. Subsequently, fuel check figures were entered on the SWORD by the commander at
0921 hrs, 0942 hrs, 0954 hrs and 1008 hrs.
As the flight continued over Northern Italy, the aircraft entered cloud and encountered some light
turbulence. Some time laterat 1029 hrs, while the commander was consulting the Flight
Management Computer (FMC), the first officer noted that G-BSNW had continued past a 'waypoint'
without following the required track to the left; at the time, the Mode Control Panel (MCP) was in
Lateral Navigation ('L Nav') mode. Additionally, the 'trend vector' started to show a turn to the right.
The first officer's initial impression was that there was a problem with the FMC and selected
'Heading' on the MCP. However, this had no apparent effect and the aircraft was now banking
increasingly to the right. With a bank angle approaching 30 to 35°, the first officer's thought was
that the autopilot had malfunctioned as the bank angle limit set on the MCP was 25°. He
disconnected the autopilot by using the switch on the control wheel and the aircraft immediately
banked further right. As the first officer countered this movement by moving the control wheel to the
left, he was also aware of the commander maneuvering the control wheel. The commander had
heard the first officer say "selecting heading select" and had looked up. Almost immediately, he
heard the first officer say "taking the autopilot out". The commander could see that they were IMC,
with a large angle of bank and that the control wheel was in a left bank attitude. He can recall
stating that he had control and remembers applying back pressure and a large left roll input to the
control wheel. The aircraft rolled wings level and began to climb; the first officer was now
just following through on the controls and giving the commander attitude information. The crew
were aware that the aircraft had diverged from its assigned level by at least 800 feet and also from
its assigned track. By now, ATC were concerned with the maneuvering of the aircraft and there was
some confusion until the aircraft was re-established at FL 290 on the required track.
The commander was now flying the aircraft manually and needed a considerable left control wheel
deflection to maintain straight and level flight. The crew checked the aircraft systems but could find
no reason to explain the situation. After discussing the predicament, the commander declared a
'PAN' and requested a diversion to Rome. Once the aircraft was heading for Rome, the first
officer suggested that he take the handling duties, thereby enabling the commander to properly
review the situation. This was agreed and, shortly afterwards, the commander noticed the fuel
imbalance. With the first officer monitoring his actions, the commander reconfigured the fuel
system to resolve the imbalance. Then, once the crew were satisfied that there was no further
problem with the aircraft and that they still had the required fuel, they cancelled both the emergency and the diversion. A normal landing was subsequently carried out at Athens at 1211 hrs.
At the time of the incident, the cabin staff were setting up the duty free trolley and some passengers
were queuing for the toilets. As the commander was recovering the aircraft from the
un-commanded roll, cabin crew members experienced a violent rolling maneuver and a sensation of
being pressed to the floor; the purser and two passengers fell to the floor. Afterwards, once the
cabin staff had ensured that all the passengers were in their seats with their seatbelts fastened, the
purser went to the flight deck. The commander informed her that the incident was under control but
that they would be diverting to Rome; she returned to the cabin to prepare for the landing and to
reassure the passengers. Shortly afterwards the commander advised her of the cause of the incident
and subsequently made a Public Address (PA) to the passengers; thereafter, once the imbalance had
been corrected, he visited the cabin to further reassure the passengers.
Accident investigation:
 |
|
Sources:
https://assets.publishing.service.gov.uk/media/5422f468ed915d13740004d3/dft_avsafety_pdf_501724.pdf
https://www.jetphotos.com/photo/10442930 (Photo)
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 04-Apr-2025 16:16 | Justanormalperson | Added |
| 04-Apr-2025 16:16 | ASN | Updated [Narrative, Accident report, ] |
Corrections or additions? ... Edit this accident description
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