Covering form of preliminary or final report

Date of event:	2022.03.11
Incident number:	CZ-22-0126
Report:	Final report
Place of event:	LKOL ATZ
Registration mark:	Accident
Weight category MTOM::	<2250 kg
Type of operation:	Recreational and sport aviation
Plane / SFM:	Sports flying machine
Type of plane / SFM:	CH 77 Ranabot
Health effects of event:	The fatal injuries
PDF document:

Description:

SUMMARY

Synopsis

On 11 March 2022, the AAII was notified of an air accident of the CH 77 Ranabot UL helicopter at LKOL ATZ. After take-off from LKOL, the pilot continued flying in the north-west direction. Witnesses saw a UL helicopter falling above the E 442 motorway feeder road, rotating around the vertical axis. Significant construction elements gradually disintegrated from the UL helicopter.

The ultralight helicopter was completely destroyed by the impact of the rotating planes into the tail beam in flight, the impact on the ground and the subsequent fire. The pilot suffered injuries incompatible with life in the UL helicopter wreckage.

Factual Information

The pilot pulled the UL helicopter out of its permanent parking place in the southern part of the LKOL before the planned flight to the area of the Dolní Morava ski resort. During pre-flight preparation, he probably filled the UL helicopter’s tanks with an unknown amount of fuel from two 20-litre fuel cans. He placed a pair of ski boots on the floor in front of the left seat and a pair of downhill skis in the space above the left seat, and wrapped the ski ends with two sweatshirts.

After taking off from the paved area in front of the garage door, the ultralight helicopter continued to fly in the north-west direction. After he overflew the E 442 motorway feeder road, a situation occurred when the main rotor blades came into contact with the tail beam. The tail beam with struts, the tail beam end section with stabilisers and tail rotor, the main rotor blades and the rear fuselage hood were gradually detached from the UL helicopter. The damaged UL helicopter, rotating around the vertical axis, began to spin spontaneously with the main rotor towards the ground. The uncontrollable UL helicopter was falling along a curved trajectory at a high angle to the ground. The ultralight helicopter first hit the ground with the main rotor head, the main rotor shaft sank into the ground, and the fuselage remained lying on the spot with the skid landing gear up. Having crashed on the ground, the helicopter caught fire. The UL helicopter wreckage affected by the fire was completely destroyed. The pilot’s charred body was found in the wreckage of the cabin. Both skis, ski boots and both sweatshirts were found in close proximity to the charred debris.

Analyses

Pilot’s Competency

The pilot was competent for VFR flying. The Commission was unable to determine how many hours the pilot had flown during the four months of operating the UL helicopter CH 77 Ranabot. Given the season of the year and information from the pilot’s acquaintance, it can be assumed that he had little experience with flying on the type and was transporting ski equipment in the UL helicopter for the first time. On the other hand, it can be confidently confirmed that he had extensive experience and solid habits in piloting the R 44 helicopter and probably did not realise how the improper use of safety seat belts could affect the CH 77 Ranabot UL helicopter’s centre of gravity. The decision to place and carry such a large load in the cabin of the UL helicopter was completely contrary to the flight manual and the fact that only one of the four items was strapped down was completely contrary to the safe conduct of the flight.

Fragments of safety seat belts were found at the air accident site, indicating that only lap belts were used to fasten the pilot and one of the skis. Three of the four shoulder strap buckles, with no signs of mechanical damage, were found outside the closed belt locks of the lap belts into which these buckles are to be normally fastened.

Pilot’s response to an unusual situation

The pilot responded to an unusual situation, which was most likely the spontaneous movement of the unfastened ski in the space above the left seat, in an inappropriate and unsafe manner. By probably letting go of the collective control lever and concentrating on handling the foreign object in the cabin, he lost control of the UL helicopter, which went into an extremely sharp descent when the main rotor and engine power parameters suddenly changed to which the pilot responded with inappropriate control intervention.

Mechanical condition of UL helicopter wreckage

During the flight, the rotating main planes came into contact with the UL helicopter fuselage, became destroyed and rendered the UL helicopter uncontrollable. The ultralight helicopter was destroyed by the forces exerted when the main rotor blades struck the tail beam, crash onto the ground at a high angle with minimal forward motion, and subsequent fire.

The technical inspection, performance of essential expert examinations and analyses, including the assessment of the technical condition of the UL helicopter critical parts discovered no proof of any technical defect that could be the cause of the air accident or could lead to the loss of power or manoeuvrability of the helicopter.

Flight Performance

As part of the air accident investigation, it was also investigated how the downhill skis and a pair of ski boots had been stored in the cabin of the UL helicopter. An UL helicopter of the same type was practically tested to verify the only possible way of storage, namely in the left seat. When using this method, the safety seat belt could only fasten one ski due to its maximum possible clamping length. The second one had to be stored freely, without any fastening. Each of the two specifically damaged sweatshirts was used on the ends of the skis to protect the cabin interior from damage. Similarly, the pair of ski boots found was, due to the limited space in the cabin, most likely stored on the floor in front of the left seat without the possibility of being secured against movement.

Critical Situation

The critical situation occurred about one minute after take-off, probably in the climb phase or transition to the horizontal flight. At this phase of the flight, the unattached ski apparently moved spontaneously. The pilot probably responded to the spontaneous movement of the unattached ski and let go of the controls to free his hands to handle the transported object. At the same time, the improper use of safety seat belts allowed his body to move freely in the pilot’s seat. These facts adversely affected the flight mode, when the UL helicopter spontaneously went into an increased power descent. Rough control intervention and inappropriate response to the symptoms of incipient drop in power, i.e., a rapid decrease in main rotor rotations typical of light rotors with low inertial forces, caused a decline in centrifugal forces on the main rotor blades with extreme blade flapping and simultaneous UL helicopter’s nose-down pitching when the main rotor blades hit the tail beam. The subsequent destruction of the main rotor, tail beam and violent transmission shaft breakage caused the UL helicopter to become uncontrollable and fall uncontrollably to the ground.

Conclusions/Causes

The cause of the air accident was pilot’s distraction during probable handling of an unsecured foreign object in the cabin shortly after take-off, which caused loss of control of the UL helicopter.

 

Attached final report in PDF file is in original Czech language.