On 11 November 2005 a further investigation under section 19DF of the Air Navigation Act 1920 was commenced into aspects of this accident. This investigation has been completed and a supplementary report 200507077 has been released and is available on the website.
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.