FACTUAL INFORMATION
In common with most transport accidents, this occurrence
involved a number of different contributing factors. Although some
of these factors were associated with actions of individuals or
organisations, it is essential to note that the key objective of an
ATSB safety investigation is to identify safety deficiencies or
weaknesses in the safety system and to learn how to minimise the
risk of future accidents. It is not the purpose or intention of the
investigation to apportion blame, or to provide a means of
determining liability.
Sequence of events
At about 0836 Eastern Standard Time on 27 November 2001, a Beech
Aircraft Corporation King Air C90 aircraft, registered VH-LQH, took
off from runway 29 at Toowoomba aerodrome, Queensland for an
Instrument Flight Rules charter flight to Goondiwindi, Queensland.
On board were the pilot and three passengers.
Just prior to, or at about the time the aircraft became
airborne, the left engine failed. A subsequent examination of the
left engine found that it probably lost thrust-producing power
almost immediately. Following the engine failure, the take-off
manoeuvre continued and the aircraft became airborne prior to
crashing.
The aircraft was equipped with an automatic propeller feathering
system, but the propeller was not feathered at impact. The reason
the propeller was not feathered could not be determined. The
landing gear was not retracted during the short flight. The right
engine was developing significant power at impact.
The aircraft remained airborne for about 20 seconds. The
aircraft's flight path was typical of an asymmetric, low speed
flight situation, and it is unlikely that the aircraft's speed was
ever significantly above the minimum control speed
(Vmca) of 90 kts. The aircraft manufacturer's specified
procedures for responding to an engine failure in LQH stated that
the take off should be rejected below the 'take-off speed',
specified as 100 kts. After control of the aircraft was lost, and
as the aircraft was rolling through about 90 degrees left bank, it
struck powerlines about 10 m above ground level and about 560 m
beyond the end of the runway. It then continued to roll left and
impacted the ground inverted in a steep nose-low attitude. An
intense fuel-fed fire erupted upon initial impact with the ground.
The aircraft was destroyed and all four occupants sustained fatal
injuries. The accident was not considered to be survivable due to
the impact forces and post-impact fire.
Maintenance-related issues
The central event in this accident was the failure of the left
engine, which was the 'critical' engine on the aircraft in terms of
aircraft performance considerations. Examination of the left engine
showed internal damage that was consistent with the fracture and
release of one or more compressor turbine blades into the engine
gas path, resulting in a significant reduction in power from the
engine. There were no indications that the engine failure was due
to manufacturing defects, metal fatigue, foreign object damage
during the flight, or the quality or quantity of fuel on board the
aircraft. Examination of the compressor turbine blades indicated
that they had been exposed to higher than normal operating
temperatures in the period leading up to the accident.
The engine failure occurred at 3,556.0 hours since the last
overhaul, which was within the 3,600 hours time between overhaul
(TBO) specified in the engine manufacturer's service bulletins.
However, the aircraft's engines were operating on a life extension
to 5,000 hours TBO in accordance with the provisions of the
Australian Civil Aviation Safety Authority (CASA) Airworthiness
Directive AD/ENG/5 Amendment 7. A requirement of the AD was that,
if the engines were operating to a 5,000 hour TBO, they had to be
subject to an engine condition trend monitoring (ECTM) program. The
pattern of ECTM data from the left engine indicated that a
potentially safety-critical problem existed in that engine for
several weeks prior to the accident. For a variety of reasons, that
evidence was not detected and analysed, nor was appropriate
remedial action initiated. Without timely intervention to address
the developing engine problem, it was increasingly probable that
the aircraft would have an in-flight emergency involving the left
engine.
The pattern of evidence suggested that a problem with the
efficiency of the cold section of the engine probably led to
temperature-related damage to the compressor turbine blades, which
probably resulted in the failure of one of those blades. However,
some other explanations for the failure, such as a previous hot
start leading to or exacerbating the temperature-related damage,
could not be discounted.
Apart from issues associated with the left engine, there was no
indication of any fault in any aircraft system that may have
contributed to the accident. The ECTM data for the right engine
suggested that a potential problem had also been developing in the
cold section of that engine for a period of time.
The last maintenance of the left engine most probably occurred
on 7 June 2001. Based on the requirements of AD/ENG/5, a compressor
performance recovery wash was required to be conducted in response
to trend monitoring parameter deviations, or at intervals not to
exceed 3 months or 220 hours, whichever came first. Had the
performance recovery wash been conducted on the left engine at the
appropriate time, it may have been effective in removing the source
of deterioration in cold section efficiency.
Prior to March 2001, maintenance on the operator's aircraft was
conducted by an external maintenance organisation. From March 2001,
maintenance was conducted by a newly formed internal maintenance
organisation. The ratio of the operator's available maintenance
personnel resources relative to the maintenance resources
reasonably required, resulted in the operator's chief engineer
experiencing a significant workload. In August 2001, the
maintenance controller left the operator and the chief engineer
took over the maintenance controller responsibilities. His workload
increased significantly when he took on these additional
responsibilities.
In addition to the level of maintenance resources, the
investigation noted that the defences within the operator's
maintenance organisation were deficient in a number of other areas.
The chief engineer had minimal preparation for his role as
maintenance controller. He had also not completed ECTM training,
and therefore the operator arranged to send the data to the engine
manufacturer's field representative for analysis. However, the ECTM
data were not being recorded or submitted for analysis as
frequently as required by the engine manufacturer's requirements or
AD/ENG/5. In addition, there were deficiencies in the operator's
maintenance scheduling processes.
CASA was aware that the chief engineer had not completed ECTM
training and that the operator had an arrangement to send ECTM data
to the engine manufacturer's field representative for analysis.
However, CASA surveillance had not detected any problems with the
operator's ECTM program prior to the accident. Following the
accident, CASA inspectors conducted a review of the engine
condition monitoring programs of operators in their region. The
review found that a number of the operators were not complying with
relevant requirements.
The introduction of AD/ENG/5 allowed life extensions to be
approved for PT6A engines in Australia under less restrictive
circumstances compared with those required by the engine
manufacturer. By allowing a wider range of operators to extend
TBOs, there was an onus on CASA to take measures to assure itself,
during its surveillance activities, that operators were complying
with the AD and conducting ECTM appropriately. However, CASA's
surveillance system was not sufficiently rigorous to ensure that
the mitigators it had introduced within AD/ENG/5 for allowing TBO
extensions were effective.
The investigation also noted that the CASA system for approving
maintenance organisations and maintenance controllers did not
appropriately consider the maintenance organisation's resource
requirements.
Flight operations issues
The investigation determined that the pilot was appropriately
licensed to conduct the flight, and that it was unlikely that any
medical or physiological factor's adversely affected the pilot's
performance. There was also no evidence that incorrect aircraft
loading or meteorological conditions were factors in the
accident.
Several factors would have contributed to the aircraft's speed
not being sufficient for the pilot to maintain control of the
aircraft during the accident flight. These factors included the
significant loss of power from the left engine just prior to, or at
about the time, the aircraft became airborne, and the substantial
aerodynamic drag resulting from the landing gear remaining extended
and the left propeller not being feathered. In addition, the
aircraft's speed when it became airborne was probably close to
Vmca and not sufficient to allow the aircraft to
accelerate to the best one-engine inoperative rate-of-climb speed
(Vyse) of 107 kts with an engine failure.
With an engine failure or malfunction near Vmca, the
safest course of action would be to reject the takeoff due to the
likelihood of the aircraft not being able to accelerate to
Vyse. Although in some cases this will mean that the
aircraft will overrun the runway and perhaps sustain substantial
damage, the consequences associated with such an accident will
generally be less serious than a loss of control after becoming
airborne.
In this case, the engine failure occurred during a critical
phase of flight, in a situation that was among the most difficult
for a pilot to respond to in a manner that would ensure a safe
outcome. In addition to the timing of the engine failure, a number
of factors could have influenced the pilot's decision to continue
with the takeoff, including the nature of the operator's
procedures, the length of the runway, and the visual appearance of
the runway and buildings beyond the runway at the time of the
engine failure.
The operator specified a rotation speed of 90 kts, which was
less than the 96 kts rotation speed specified by the aircraft
manufacturer for King Air C90 aircraft. The operator's specified
rotation speed had the effect of degrading the one-engine
inoperative performance capability of the aircraft during takeoff.
In addition, the operator's procedures did not provide appropriate
guidance for pilots regarding decision speeds or decision points to
use for an engine failure during takeoff.
While aircraft manufacturers have provided guidance material in
operating manuals regarding engine failures leading to power loss
in multi-engine aircraft, CASA had not published formal guidance
material. The level of training available for emergencies in this
category of aircraft during critical phases of flight and at high
aircraft weights was less than desirable.
Toowoomba aerodrome was licensed and met the relevant CASA
standards. However, runway 29 did not meet the ICAO standard in
relation to the runway end safety area (RESA).
Safety action
Since the accident, CASA has made changes to the requirements of
AD/ENG/5 and the processes for assessing the suitability of
maintenance controllers.
As a result of this investigation, the ATSB issued six
recommendations to CASA relating to the following areas:
- reviewing operator compliance with the requirements of
mandatory turbine engine condition monitoring programs.
- surveillance processes for confirming operator compliance with
mandatory engine condition monitoring programs.
- processes for identifying priority areas for consideration
during airworthiness surveillance and approval activities.
- processes to assess whether a maintenance organisation has
adequate resources to conduct its required activities.
- the provision of formal advisory material to operators and
pilots about managing engine failures and other emergencies during
takeoff.
- the assessment of synthetic training devices for the purpose of
training pilots in making decisions regarding emergencies during
critical stages of flight.
As a result of this accident, the ATSB has issued a
recommendation to the aerodrome operator for it to liaise with CASA
to evaluate an engineering solution to enhance aircraft
deceleration in the runway end safety area of runway 11/29 at
Toowoomba aerodrome.
A number of issues identified during the investigation related
to the aircraft operator, and would normally have resulted in
safety recommendations to that organisation. However, subsequent to
the accident the operator ceased operations.