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.
