FACTUAL INFORMATION1
History of the flight
On 20 August 2005, at about 1340 Central Standard Time, a
British Aerospace 146-300 (146-300) aircraft, registered VH-NJN,
with a crew of five and 60 passengers, was being operated on a
scheduled passenger service from Cairns, Qld, to Alice Springs, NT.
The first officer was the handling pilot for the visual approach
and landing to runway 12 at Alice Springs Airport.
The flight crew reported that, at about 50 ft above the ground,
the aircraft rate of descent (ROD) increased significantly from
what had previously been a 'normal' approach. Despite the initial
reaction by both flight crew members to arrest the increased ROD by
increasing the nose-up pitch attitude of the aircraft, and
subsequently the engine thrust, the aircraft landed heavily and
bounced into the air. The captain commanded a go-around for a
second landing on runway 12. During the go-around, the flight crew
reported to air traffic services that there was 'a fair bit of
shear just at the touchdown point.'
A subsequent engineering inspection of the aircraft identified
damage to the tailscrape indicator (Figure 1), indicating that a
tail strike had occurred. There were no reported injuries to the
crew or passengers, and there was no significant damage to the
runway surface or other facilities.
Figure 1: Damaged aircraft tailscrape
indicator
Operational information
The flight crew were appropriately qualified for the flight.
Both pilots reported being fit and well at the time of the
occurrence.
No evidence was found of a defect in the aircraft or its systems
that may have contributed to the circumstances of the occurrence.
Examination of the aircraft load sheet indicated that the planned
aircraft landing weight was 35,785 kg, and that the centre of
gravity was within limits. The flight crew reported calculating the
actual aircraft weight for the landing as 37,300 kg. As a result,
the flight crew applied the 38-tonne Landing Card to their approach
planning. That resulted in a final approach speed (VAPP)
of 124 kts, and a landing flaps reference speed (VREF)
of 119 kts.
Weather information
The Alice Springs Terminal Aerodrome Forecast indicated a wind
of 150 degrees true at 13 kts and CAVOK2 conditions. The
forecast ambient temperature was 17°C, and the forecast mean sea
level (MSL) pressure was 1025 hectopascals (hPa). The area forecast
indicated a forecast wind at 3,000 ft above mean sea level (about
1,200 ft above ground level (AGL)) of 150 degrees true at 20 kts,
nil significant cloud, fine weather, and good visibility.
Automatic Terminal Information Service (ATIS) 'Echo' was current
at the time of the occurrence. That information included that the
surface wind was 090 degrees magnetic at 15 kts, CAVOK conditions
were present, the ambient temperature was 17°C, and the MSL
pressure was 1023 hPa. ATIS 'Echo' provided no indication of any
wind gusts that might have affected operations at Alice
Springs.
Observations of the meteorological conditions at Alice Springs
were recorded by a Bureau of Meteorology (BoM) Automatic Weather
Station (AWS). The AWS was located near the wind sock on the south
side of, and near the middle of runway 12/30. Reports from the AWS
were available to pilots from air traffic services by radio, or by
telephone. The 1330 AWS observation indicated a surface wind of 110
degrees magnetic at 7 kts and gusting to 11 kts, CAVOK conditions,
an ambient temperature of 17°C, a dewpoint3 of 2.1°C, and MSL
pressure of 1022.6 hPa. In addition, data from a weather balloon
flight conducted at Alice Springs at 1430 indicated a generally
east-north-easterly wind at less than 10 kts up to a height of
about 1,000 ft AGL.
The flight crew subsequently reported that they experienced
nothing during the approach that was contrary to the forecast
conditions, or to the information provided on the ATIS until about
50 ft AGL. The captain reported the presence of 'a definite
under/overshoot wind shear' during the final approach, but that it
was not as strong as he had experienced previously at Alice
Springs.
The pilot of a Cessna Aircraft Company 210 (C210) that landed on
runway 12 shortly after the 146-300, subsequently reported that he
experienced gusty wind conditions during the initial landing
approach, but that they were not outside the operational limits for
the C210. In addition, that pilot reported being surprised that it
was 'not that windy', and that he did not experience any turbulence
at touchdown on runway 12.
A BoM aftercast
4 concluded that:
The situation [at Alice Springs] did not appear conducive to
windshear. A high pressure system west of Perth extended a strong
ridge across central Australia. With fine stable conditions and
moderate south to south-east winds.
Instrument Landing System (ILS) and 'T' visual approach slope
indicator system (T-VASIS) approach aids were available for
approaches to runway 12 at Alice Springs. The T-VASIS approach aid
provided 3° visual approach guidance to the touchdown point on the
runway. The flight crew reported that the approach was flown
visually, using the ILS as back-up reference, and that the aircraft
was stabilised on the approach until reaching 50 ft above the
runway. No evidence was found to suggest that the aerodrome, its
facilities, or the characteristics of the runway influenced the
circumstances of the occurrence.
Recorded data
The aircraft was fitted with a Plessey PV1584M Data Acquisition
and Recorder Unit. The recorded flight data was examined by the
Australian Transport Safety Bureau to establish the factors that
led to the tail strike. The recorded data for the final approach
below 500 ft radio altitude5 (RADALT)
is represented at Figure 2. The aircraft's recorder installation
did not include the option to record the presence of any
windshear.
Examination of the available recorded data for the final
approach below 500 ft RADALT revealed that the aircraft's pitch
attitude alternated between 0 to 2.6° nose-down. The variations in
the aircraft's attitude were accompanied by periods of varying
indicated airspeed, including from a maximum of 133 kts at 223 ft
RADALT, reducing to 120 kts at 49 ft RADALT, and 113 kts at 10 ft
RADALT. Those reduced speeds appeared to reflect the planned vREF
of 119 kts and anticipated touchdown speed of 112 kts. The
glideslope angle and localiser deviation were examined and found to
be within the expected range for the final approach.
The aircraft's ROD was derived from the recorded data. That
derived data revealed that the aircraft's ROD varied during the
final approach as follows:
- the average ROD was 690 ft/min until passing 300 ft RADALT
- below 300 ft RADALT, the average ROD was 630 ft/min
- the instantaneous ROD in the 2 secs immediately prior to
touchdown, or below 21 ft RADALT was 657 ft/min, or 11 ft/sec.
The recorded aircraft pitch attitude data indicated that the
flare was commenced at 21 ft RADALT.
Figure 2: Recorded data selected parameters below 500 ft
RADALT
There was a one-second discontinuity in the recorded data on
touchdown, which was considered to be consistent with the tail
strike occurring at that time. Immediately prior to that
discontinuity, the aircraft's derived nose-up pitch rate was 5.8
deg/sec. At that rate of nose-up pitch, interpolation of the
missing data indicated the potential for the aircraft's nose-up
pitch attitude with the main landing gear compressed to have been
greater than 7°.
On the recommencement of the recording, the aircraft's pitch
attitude was 6.7° nose up and the main landing gear was compressed.
The nose landing gear was not recorded as touching the runway.
Organisational information
The company's Operations Manual stipulated the following
requirements affecting the calculation of an aircraft's
VAPP:
- VAPP = V REF + 5 kts + an additional
factor (in kts) to take account of any reported wind gusts,
turbulence and windshear. The maximum additional factor for
application by flight crews was 9 kts. - The recommended additional gust factor for application by
flight crews equalled half the reported wind speed gust.
The flight crew reported that based on the content of ATIS
'Echo', an additional factor was not applied to the interpretation
of vAPP in this instance.
The risk of an aircraft sustaining a landing tail strike is
elevated if the aircraft is subjected to an unstabilised final
approach for landing, which can include turning onto final approach
with excessive airspeed, altitude, or both. The definition of a
stabilised approach in the company's Operations Manual included
that:
- the aircraft must be stabilised in the landing configuration by
400 ft above airport level - for visual approaches, the aircraft was not greater than one
dot high or low on the T-VASIS - the aircraft was established on the runway centreline with only
small changes in heading or pitch required to maintain the approach
path - the aircraft's speed was not above VAPP + 10 kts and
not less than VAPP - 5 kts - ROD was required to be not greater than 1,000 ft/min
- momentary excursions of slope and speed, caused by wind gusts
or turbulence, were acceptable.
The operator's Training Manual included that:
- flight crews should aim to cross the runway threshold at 50 ft
above the touchdown elevation at VREF - touchdown was anticipated at approximately VREF - 7
kts - the touchdown should usually be achieved at a pitch attitude of
4 to 5° nose-up, and that the aircraft's pitch attitude must not
exceed 8° nose-up in the flare.
The operator reported that there was no specific mention in the
Training Manual, or the Operations Manual of the risk of tail
strike in the company's 146-300 aircraft.
The aircraft manufacturer had promulgated preliminary notes
regarding tail strikes during takeoff and landing in the 146-300
aircraft. Those notes included that the risk of a tail strike
during landing was elevated if:
- A late flare was initiated by a flight crew while their
aircraft was experiencing a high sink rate that would result in a
heavy landing. That implied a nose-up attitude of about 8° at
touchdown and a ROD of in excess of 10 ft/sec. The manufacturer
indicated that a typical landing pitch attitude was about 2 to 3°
nose-up. - Maintenance of the required airspeed was inaccurate from the
'screen height' of 50 ft until touchdown. The manufacturer
commented that if that airspeed was allowed to decay excessively,
the pitch attitude could become critically close to tail strike
angles. The manufacturer's notes concluded that:
On the 146-300 [and RJ100] pitch angles in excess of 5 degrees
should be avoided and angles in excess of 7 degrees with the oleos
compressed may result in a tailstrike.
- Only those investigation areas
identified by the headings and subheadings were considered to be
relevant to the circumstances of the occurrence. - Visibility, cloud and present
weather better than prescribed values or conditions - ICAO Doc
8400, 24 November 2004. - Temperature at which, under ordinary
conditions, condensation begins in a cooling mass of air. - A retrospective statement of
anticipated meteorological conditions affecting a given place
during a specified period, which can include the interpretation of
recorded radar data, synoptic observations, recorded AWS data, and
other available sources of recorded meteorological
information. - An indication of the height of the
aircraft above ground level (AGL). Approximates the theoretical
concept of 'absolute altitude', which is the distance along a local
vertical between an aircraft and a point on the ground where the
local vertical cut's the earth's surface.