History of the flight
At approximately 0830 EST, the pilot of the Bell 47G-4A turbine-powered (Soloy) helicopter, registered VH-MTX, was conducting a lift-off to the hover from a mobile helicopter landing site (HLS)1 at Caboolture aerodrome, when the helicopter rolled onto its right side. Weather conditions at the time of the occurrence were reported to be '…little or no wind, warm and humid, some cloud but clearing.' The helicopter was substantially damaged and there was no post-occurrence fire. The pilot, who occupied the left seat2, was fatally injured and the passenger, who occupied the right seat, sustained minor injuries.
Pilot in command
The pilot held an Airline Transport Pilot (Helicopter) Licence, a Commercial Pilot (Aeroplane) Licence, a Command Multi Engine Instrument Rating (CMEIR) (Helicopter), a CMEIR (Aeroplane), and a Grade 1 Instructor (Helicopter) Rating. According to his pilot flying logbooks, he had accumulated approximately 8,293 hours total flying experience, of which approximately 7,180 hours was on helicopters, including 14.8 hours on the Bell 47G helicopter type. He had flown 2.0 hours in the last 30 days and 15.7 hours in the preceding 90 days. His last flight prior to the occurrence flight was nine days previously in a Bell 206 type helicopter. He had last flown a Bell 47G type helicopter on 19 December 2002, including taking off from and landing back on the mobile platform involved in the occurrence. He had not previously flown a turbine-powered Bell 47G helicopter.
The pilot was endorsed to fly Bell 47G type helicopters in accordance with Section 40.3.0 of the Civil Aviation Orders (CAO). In accordance with paragraph 3.3 of those orders, he was permitted to fly turbine-powered Bell 47G helicopters without further endorsement. The operator also reported that, in accordance with paragraph 3A.4 of CAO 40.3.0, prior to the occurrence flight, the pilot was offered refresher training in the turbine-powered Bell 47G type, however the pilot declined that offer.
The pilot met the recency requirements of Civil Aviation Regulation 5.178, having completed CMEIR (Helicopter) and Instructor (Helicopter) Rating renewals on 13 May 2002, in a Bell 412 helicopter type.
Due to the nature of his employment, the pilot had flown 10 aircraft types in the preceding 12 months, of which 7 were helicopters. Those helicopter types included a mix of European and North American types, a mix of single engine and multi-engine types3, and a mix of turbine and piston engine types. Most of the pilot's helicopter flying experience was in turbine engine types. The pilot was experienced in operating helicopters from mobile platforms.
The passenger was employed by the same organisation as the pilot in command. He was an experienced helicopter pilot, who reported that he had accumulated approximately 4,700 hours total flying experience, of which approximately 4,500 hours was on helicopters. He reported that he was not in current flying experience. According to witnesses, he did not have his hands or feet near the flying controls during the occurrence.
The pilot's aviation medical certificate was valid and carried a restriction for him to have available reading vision correction. A review of his medical records, investigation interviews, results of the post-mortem examination and toxicological testing, found no evidence of pre-existing medical conditions or the presence of any substance that may have influenced his performance.
Four-point restraint harnesses with inertia reel shoulder straps were fitted at the pilot and right side passenger positions. Post-occurrence technical examination revealed that they were firmly secured to their mounts, and the inertia reels appeared to operate normally. The pilot occupied the left seat and remained restrained during the rollover sequence. He sustained severe impact injuries to the rear of the upper torso and lacerations to the back of the head.
Type: Bell 47 helicopter
Model: 47G-4A (Soloy)
Serial Number: 7765
Year of manufacture 1971
Engine: Rolls Royce 250-C18
Total time in service: Approximately 5,570 hours
Maintenance release: Number 09425 issued 14/03/03 at 5,549.7 hours
The helicopter had been imported from Japan in October 2002, receiving an Australian Certificate of Airworthiness in December 2002. The helicopter was maintained in accordance with the manufacturer's and CASA approved documents and schedules, and had flown approximately 20 hours since its last 100-hourly inspection.
Damage to the helicopter
The helicopter came to rest on its right side, with its right skid landing gear resting on the right rear corner of the platform. The canopy bubble had shattered. The main rotor, mast and transmission assembly had detached from the helicopter as a single unit and was located next to the helicopter. The 'white' main rotor blade4 was lying across the cockpit. Evidence, in the form of multiple main and tail rotor impact marks, was observed in the ground with an area of burned grass beneath the helicopter's engine exhaust. One of the tail rotor blades had detached and was located approximately 30 metres from the helicopter. The tip of the 'red' main rotor blade was found approximately 150 metres to the east of the helicopter. Both arms of the main rotor stabiliser bar had fractured and were found within 20 metres of the helicopter. All major components were located and identified at the site. Post-occurrence technical examination of the helicopter did not reveal any evidence of an airframe, engine or system fault that may have contributed to the accident.
Mobile platform information
The mobile platform was a flat-based metal construction on wheels, measuring 365 x 300 cm and was approximately 22 cm above the ground. A 5 cm high metal lip ran along both sides of the platform. There were no metal lips at the front or rear of the platform. The front wheels were positioned forward of the base and were approximately 27 cm in diameter. The rear wheel axles were in line with the platform base, allowing the 38 cm-diameter wheels to sit approximately 18 cm above the base. There were two prominent worn strips along the base approximately 38 cm from the side lips, which indicated the usual positioning of the helicopter skids on the platform. At the time of the occurrence, the platform was connected to a small tractor. The tractor brake was engaged and there was no evidence of the tractor having moved throughout the accident sequence.
Civil Aviation Regulation 92 (1) states that:
An aircraft shall not land at, or take-off from, any place unless:
(d) the place… is suitable for use as an aerodrome for the purposes of the landing and taking-off of aircraft;
and, having regard to all the circumstances of the proposed landing or take-off (including prevailing weather conditions), the aircraft can land at, or take-off from, the place in safety.
GEN 2.2 of the Aeronautical Information Publication, defines an aerodrome as:
A defined area of land or water (including any buildings, installations and equipment) intended to be used either wholly or in part for the arrival, departure and movement of aircraft.
Guidelines for the establishment and use of HLS are at Civil Aviation Advisory Publication (CAAP) 92-2 (1), which defined an HLS as:
…a place that may be used as an aerodrome for the purposes of landing or taking off of helicopters.
The definition of '…place…' in CAAP 92-2 (1) included '…on a structure…'.
There is no CASA regulation or guidance concerning the design or use of mobile platforms. Additionally, international standards and recommended practices contained in Annex 14 to the International Civil Aviation Organization (ICAO) Convention on International Civil Aviation, Aerodromes, Volume II - Heliports, do not refer to mobile platforms. A search of international regulatory authorities found no documentary guidance regarding design or use of mobile platforms.
The investigation found that mobile platforms of varying design are used throughout the Australian civil helicopter industry. Some of those designs incorporated side lips and others had no protrusions above the platform surface. Most of the platforms were tractor-towed.
Damage to the mobile platform
Examination of the mobile platform revealed two fresh scratch marks on the right lip approximately 50-85 cm from the rear of the platform. Also evident were fresh gouges on the rear edge of the platform, adjacent to the right wheel axle, which indicated that the helicopter had been moving rearwards as it contacted the lip. Examination of the platform did not reveal any evidence of it having moved throughout the rollover sequence.
Pilot employees from the same organisation as the occurrence pilot reported that they each received funding for up to 40 flying hours each financial year to maintain recency on selected aircraft types. They also reported that, due to the nature of their employment, some pilots had a requirement to maintain recency on a number of types simultaneously.
The phenomenon known as dynamic rollover was described in helicopter textbooks, training manuals and industry and safety publications. It was included at:
- items 10.7 and 12.1 of the CASA Day (VFR) Syllabus - Helicopters, Issue 3, January 1999, which applied from Student through to Commercial Helicopter Licence standard
- item 2.1.14 of the Air Transport Pilot (Helicopter) Licence - Aeronautical Knowledge Syllabus, Issue 3, January 1999.
Dynamic rollover has been defined as:
The occurrence of a rolling motion, while any part of the landing gear is acting as a pivot that causes the aircraft to exceed a critical angle and roll over5.
Another definition states that:
Put simply, dynamic rollover is the result of the helicopter developing excess angular momentum about the skid in contact6...
Dynamic rollover typically occurs when a critical rollover angle is exceeded. That angle is dependent upon control limits and in most helicopters is in the order of 15 degrees. Accidents attributed to dynamic rollover have occurred previously on a number of surfaces, including open flat grassed surfaces.
Post-occurrence technical examination of the helicopter did not reveal any evidence of an airframe, engine or system fault that may have contributed to the accident. In addition, examination of the mobile platform did not reveal any evidence of it having moved throughout the rollover sequence.
The circumstances of the accident are consistent with the phenomenon known as dynamic rollover. Scrape marks from the helicopter's right skid were found on the lip along the right side of the mobile platform. That indicated that the helicopter was not raised to a height sufficient to clear the platform in the event of lateral movement. There was no wind reported at the time of the occurrence that could have contributed to the lateral movement. The pilot had extensive flying experience and normally flew a mix of different types, including a mix of European and North American types. Due to that experience, the investigation considered that confusion with respect to correct flight control input to control yaw was unlikely.
If the pilot had prevented the lateral movement of the helicopter during the lift off to the hover, and had raised the helicopter to a hover height sufficient to clear the platform, dynamic rollover would most probably have not occurred. Therefore, the investigation considered that the design or use of the mobile platform was not a factor in the occurrence.
The pilot had not flown a Bell 47 type helicopter during the preceding three months, and had not previously flown a turbine-powered Bell 47. It is likely that the pilot's lack of recency in the helicopter type, combined with his not having flown a turbine-powered Bell 47 previously, contributed to his:
- not making sufficient flight control input to correct the right lateral movement during the lift-off to the hover
- not raising the helicopter to a hover height sufficient to prevent contact with the platform.
The pilot's injuries were consistent with him being struck by the main transmission assembly as it separated from its mount as a result of the dynamics associated with main rotor ground contact.
- The pilot was not recently experienced on the occurrence helicopter type.
- The pilot in command allowed the helicopter to move laterally during the lift-off to the hover.
- The pilot in command did not raise the helicopter to a hover height sufficient to prevent contact with the mobile platform.
As a result of this occurrence, the Australian Transport Safety Bureau highlights to the helicopter industry articles regarding helicopter dynamic rollover, including:
- Advisory Circular 90-87, Helicopter Dynamic Rollover, FAA. 1986.
- Preventing Dynamic Rollover, Major Joseph H. Schmid, Flight Safety Foundation, Helicopter Safety, Volume 14, No.1, January/February 1989.
- Dynamic Rollover: A new look at an old problem, CASA Flight Safety Australia, April 1999.
- Dynamic Rollover, Peter Rogers, Heli-News Australasia, May 2003.
mobile HLS is referred to in this report as the 'mobile
2 VH-MTX was flown from the left seat.
3 The main rotor of these types rotate in the opposite directions, which require different ant-torque flight control input.
4 Helicopter rotor blades are identified by a colour-coding system for maintenance purposes.
5 Flight Safety Australia, April 1999, pp33-34.
6 Done in: Dynamically, Captain J.P. Cress, USMC, Naval Postgraduate School.
|Date:||19 March 2003||Investigation status:||Completed|
|Time:||0830 hours EST||Investigation phase:|
|Location:||Caboolture, (ALA)||Investigation type:||Occurrence Investigation|
|State:||Queensland||Occurrence type:||Loss of control|
|Release date:||26 February 2004||Occurrence class:||Operational|
|Report status:||Final||Occurrence category:||Accident|
|Highest injury level:||Fatal|
|Aircraft manufacturer||Bell Helicopter Co|
|Type of operation||Flying Training|
|Damage to aircraft||Substantial|
|Departure point||Caboolture, QLD|
|Departure time||0830 hours EST|
|Role||Class of licence||Hours on type||Hours total|