The crew of an aircraft awaiting takeoff clearance reported that a departing Boeing 737-400 struck its tailskid during rotation. That information was passed to the Tower Controller, however there was a delay of almost 12 minutes in relaying the advice to the flight crew while the runway was inspected to confirm that a tail strike had actually occurred.
The crew of the 737-400 reported that they had felt a thump during the rotation but believed it was the sound of an oleo leg bottoming. Shortly after the tailskid contacted the runway surface, the aircraft's Master Warning System (MWS) drew the crew's attention to faults in the hydraulic and flight control systems. The initial part of the climb was therefore taken up with the Quick Reference Handbook (QRH) Non-Normal Checklists concerned with the hydraulics problem, in addition to normal departure procedures.
Shortly after takeoff, the Cabin Services Manager informed the pilot in command that the rear cabin crew had heard a bump during during the takeoff. However, the pilot in command believed this was related to the hydraulic problem. The Cabin Services Manager later passed on additional information describing the sound as a "metallic scraping noise". At that time the aircraft was climbing through flight level 320 and was fully pressurised. The possibility of a tail strike was further indicated to the flight crew when they were informed by air traffic control (ATC) that there had been some pavement damage to the runway from which they had departed. The QRH procedure for a tail strike on takeoff was to ensure that the aircraft was not pressurised in case of possible structural damage. However, the procedure was reliant upon the flight crew being immediately aware that a tail strike had occurred. It did not give guidance on a course of action when the tail strike was not recognised until after the aircraft was pressurised. As it was then only 25 minutes before the aircraft would be commencing descent (at which time the depressurisation process would commence) and the pressurisation system was operating normally, the PIC elected to continue the flight to Adelaide.
Maintenance personnel inspected the aircraft on arrival and confirmed a tail strike. No damage was sustained by the tailskid except removal of paint. The hydraulic systems were also checked but no fault could be found. During the subsequent departure from Adelaide there was a recurrence of the hydraulic fault. Indications of Hydraulic System "A" low pressure and "Flight Control" low pressure were a repetition of the faults experienced on departure from Melbourne. It was subsequently determined that a hydraulic reservoir T-piece was clogged where it metered the "A" system and was the cause of the pressure fluctuations. Analysis of the Flight Data Recorder (FDR) data determined that the MWS activated in response to low pressure in hydraulic system "A" while the landing gear was in its retraction cycle and was not connected to the tail strike event.
Boeing data (Airliner, Jul-Sep 1994) suggested that the most common factors in takeoff tail strike events are excessive rotation rate and early rotation. Information from the operator's Flight Crew Training Manual indicated that takeoff and initial climb performance depend on rotating at the correct airspeed and proper rate, to the rotation target attitude. Rotation should be smooth and at an average pitch rate of 3 degrees per second. A body attitude of 9 to 10 degrees would be achieved in approximately 2.5 to 3 seconds with all engines operating, with liftoff occurring at a pitch attitude of 9.1 degrees. When the rotation rate exceeded 3 degrees per second, the minimum tail clearance decreases, and may result in contact with the ground. The minimum tailskid clearance on a normal "flaps 5" takeoff should be approximately 58 cm and occurs after liftoff. This is a consequence of the aircraft geometry and the dynamic forces that are acting after rotation has been initiated.
Analysis of FDR data for the incident indicated that rotation commenced at the correct indicated airspeed of 144 kts. The recorded data also showed that the aircraft had been subject to a rapid rotation during the liftoff period. From nose wheel off the ground to the main wheels leaving the ground, the average rotation rate was 4.3 degrees per second.
The incident occurred on the first sector of the day, the pilot in command was the handling pilot and was very experienced on the Boeing 737-400. The takeoff was conducted from runway 27 with a surface wind of 150-180 degrees at 5-12 kts. The aircraft was therefore subject to approximately 10 kts of crosswind and up to 3 kts of tailwind during the takeoff roll. Analysis of FDR data confirmed that during the 7 seconds prior to rotation the wind effect on the aircraft changed from 3 kts of headwind to 3 kts of tailwind.
A combination of wind effect and aircraft mishandling was the most likely reason for the rapid rotation that led to the tail strike. As the aircraft was subject to 10 kts of crosswind and 3 kts of tailwind during the takeoff, it was considered possible that this knowledge may have induced the pilot in command to incorrectly anticipate aircraft response to control input. Furthermore, the change in wind effect just before rotation, although not a significant amount (approximately 6 kts), may still have had an effect on the control feel and/or resulted in a marginal reduction in lift at that crucial phase of the takeoff.
As the aircraft was fully pressurised and climbing through flight level 320 when ATC informed the crew of the pavement damage, the crew were clearly unaware of the tail strike before receiving this information. Following lift-off, the almost immediate distraction of the MWS and the need to consult the QRH may have, at the very least, diverted the crew's thought processes at a busy time. The rapid but normal climb that followed and the delay in receiving ATC confirmation of the tail strike possibly guided the pilot in command toward his decision to continue the flight rather than return to Melbourne.
Communicating with ATC is just one of the many tasks that are required of the crew during the period immediately after takeoff. It can be a demanding phase of flight and controllers are aware of minimising transmissions to the crew during this phase. However, a more timely report to the crew from ATC may have enhanced the flight crew's situational awareness. This would have allowed them the benefit of additional information on which to decide a course of action.
This incident highlighted the fact that the aircraft operator's/manufacturer's Non-Normal Checklist may not be able to deal specifically with every conceivable variation in a non-normal situation that may arise during the course of a flight. Pilots are therefore required to use their judgement in order to ensure the safety of the aircraft.
|Date:||29 November 2000||Investigation status:||Completed|
|Time:||1538 hours ESuT|
|State:||Victoria||Occurrence type:||Ground strike|
|Release date:||20 December 2001||Occurrence class:||Operational|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
|Aircraft manufacturer||The Boeing Company|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure point||Melbourne, VIC|
|Departure time||1638 hours ESuT|
|Role||Class of licence||Hours on type||Hours total|