|Title:||Pitch control problems, Boeing 747-436, G-BNLB|
|Micro summary:||Flight control system problems affected pitch control on this Boeing 747-436.|
|Event Time:||2000-02-25 at 0250 UTC|
|Publishing Agency:||Aircraft Accident Investigation Board (AAIB)|
|Publishing Country:||United Kingdom|
|Site of event:||Cruise|
|Departure:||Executive Airport, Orlando, Florida, USA|
|Destination:||Gatwick Airport, London, England|
|Airplane Type(s):||Boeing 747-436|
|Type of flight:||Revenue|
|Executive Summary:||The aircraft was operating a scheduled public transport flight from Orlando (USA) to London Gatwick. Take off was at 0110 hrs and shortly after reaching the top of climb, at FL370, the flight deck crew noticed that the Vertical Speed indication displayed on each pilot's Primary Flight Display (PFD) was fluctuating around ±200 feet per minute. The actual altitude deviation during these fluctuations was not great, being less than 100 feet. The crew were aware that other aircraft in the area were experiencing clear air turbulence, so they initially regarded these fluctuations to be weather related. The cabin crew reported that some passengers were feeling the effects of airsickness. |
When the commander left his seat to take his middle break (in cruise flight), he noted that the motion at the rear of the flight deck felt different to normal. He instructed the two first officers to disengage the autopilot, check the aircraft trim, then re-engage a different autopilot. This was complied with, but the intermittent pitch oscillations continued to occur, such that the Vertical Speed indications fluctuated around ±300 feet per minute.
During the course of the flight, each of the three autopilot systems was used in turn, but the pitch disturbances continued to occur at irregular intervals. The commander and the first officer each tried a period of manual aircraft handling but the pitch disturbances continued to occur, with the aircraft's pitch response apparently being somewhat out of phase with the manual control inputs. The commander reported that, during manual handling, the control column felt very stiff to move in the required direction and, after the exertion of considerable pressure, would become free and the aircraft would respond immediately, then requiring opposite control input. This 'notchy' feel resulted in a degree of overcontrolling.
The crew contacted the operator by satellite telephone link to advise them of the problem and were then advised that holding delays were expected on arrival at London Gatwick. In view of the commander's concern over the possible effects of the pitch control phenomenon during the landing flare, and to avoid any undue delay to the approach, he decided to declare a 'PAN' status with ATC. The aircraft was then afforded a priority approach and a dedicated ATC service on a discrete frequency.
The cabin crew were instructed to brief the passengers to adopt the 'brace' position for landing, as a precaution in the event of a heavy landing. The Emergency Landing Checklist was actioned as the aircraft came onto the base leg for landing on Runway 26L at Gatwick and the appropriate cabin announcements were broadcast during final approach.
The commander briefed the first officer to assist with the pitch flight control inputs during the landing and a smooth and accurate touchdown was achieved at 0852 hrs. The aircraft taxied clear of the runway and stopped to liaise with the attending Airport Fire Service. After discussion, the fire service was stood down and the aircraft began to taxi towards the parking stand.
At that time, the door 5L flight attendant called on the interphone system to indicate that there was smoke present in the cabin. The Airport Fire Service was re-alerted and returned to the aircraft. After external inspection found no abnormal indications, the aircraft again taxied towards the parking stand, with the fire service in attendance. During taxi, the fire service reported some smoke coming from number 4 engine, so the crew shut it down. The aircraft's APU was not started during the taxi in.
After the aircraft was parked on stand, the fire chief entered the aircraft cabin for a visual inspection of the rear cabin area and declared it safe, prior to passenger disembarkation. A member of the operator's pilot management team observed the aircraft's touchdown and subsequently indicated that the landing had generated a lot of tyre smoke at touchdown. A number of unrelated defects were recorded in the aircraft's Technical Log after this flight.
|Learning Keywords:||Operations - Upset - Uncommanded or excessive Pitch|
|Systems - Flight Control System|
|Close match:||Loss of Pitch Control on Takeoff, Emery Worldwide Airlines, Flight 17, McDonnell Douglas DC-8-71F, N8079U, Rancho Cordova, California, February 16, 2000|
|Elevator failure, Douglas DC-8-71, March 11, 1997|
|Severe pitch oscillations, McDonnell Douglas MD-11, November 25, 2000|
|Elevator control problems, Boeing - Canada (de Havilland) DHC-8-102, March 12, 2000|
|Pitch control problems, Boeing 767-300, March 27, 2001|
|Pitch control problems, BAe 146-200, G-JEAX, December 12, 2002|
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