Covering form of preliminary or final report
| Date of event : | 2021-03-30 |
| Incident number : | CZ-21-0101 |
| Report : | Final report |
| Place of event : | field near the village of Dobřichovice |
| Registration mark : | Accident |
| Weight category MTOM: : | <2250 kg |
| Type of operation : | Recreational and sport aviation |
| Plane / SFM : | Sports flying machines |
| Type of plane / SFM : | CH 77 Ranabot |
| Health effects of event : | The fatal injuries |
| PDF document : | 
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Description:
SUMMARY
Synopsis
On 30 March 2021, the AAII was notified of an air accident of the CH 77 Ranabot UL helicopter on a field near the village of Dobřichovice. The pilot with another person on board (hereinafter the passenger) carried out a recreational navigation flight. Due to the activation of acoustic warning signal informing about remaining fuel for 15 minutes of flight, the pilot carried out precautionary landing into the terrain at the eastern edge of Dobřichovice. After landing, he contacted the service organisation technician by phone asking how to set up the indicated amount of fuel on the Flybox Mini EIS electronic device. The pilot reset the data and the audible alarm stopped.
He restarted the engine and took off. Shortly after take-off, witnesses saw the UL helicopter flying horizontally first and then nose-diving while rotating around its longitudinal axis. The UL helicopter crashed onto the ground at a sharp angle. Upon an impact, both main rotor blades were forcibly detached from the rotor head and the deformed fuselage bounced shortly and fell about 10 m from the point of impact.
The crew suffered injuries incompatible with life in the UL helicopter wreckage. The UL helicopter was totally destroyed.
Factual Information
Having prepared the UL helicopter for flight, including refuelling, the pilot and the passenger boarded the cabin and fastened their four-point seat belts. After taking off at 10:42 from the permanent parking site, the pilot continued flying east, made a 360° turn over the village of Zadní Třebáň and continued flying above the valley of the river Berounka towards Dobřichovice. Here, in the area between the western and northern edge of the village, he performed a horizontal figure-eight manoeuvre and having flown a short distance above the river Berounka eastward, continued flying above the valley between the hills Červená hlína and Kámen in the south-east direction. After an overflight of the village of Čisovice, the pilot made two 360° turns above its southern edge and flew back to the D4 highway on the same route. Approx. 2 km south of the village of Řitka, he made a stopover on a meadow and shut off the engine at 11:12. After restarting the engine, he took off at 11:15 and continued flying in the north-west direction above forests north-west of the D4 highway. In this area, he made a 180° turn, overflew Řitka and landed at its eastern edge without shutting off the engine. After approx. one minute on the ground, he continued flying above the valley between the hills of Červená hlína and Kámen. At 11:30, he landed on a meadow at the eastern edge of Dobřichovice. After landing, the pilot opened the door of the UL helicopter and was communicating by phone with a service technician.
At 11:38, the pilot took off from the place of stopover at the eastern edge of Dobřichovice. Following a short run in the eastern direction, he continued climbing smoothly and performed a 180° turn. After he completed the turn, when climbing 2 m∙s-1, at the level of 300 m GPS and at the speed of 65 kt GPS, the flight mode changed suddenly. The UL helicopter abruptly pitched down and started descending sharply to the ground in the right rotation around its longitudinal axis. After seven seconds, it hit the ground and bounced off. Following a short bounce and a hard impact, it disintegrated.
Analyses
The pilot was competent for VFR flying. In 17 months of operating the UL helicopter CH 77 Ranabot, had flown 14 hours and made 92 flights. He thus had little practical experience with flying on the given type, In most cases, he flew without another person on board and according to the aircraft logbook entries, these were short 5-to-10-minute flights.
The pilot’s inconsistent approach to performing important pre-flight tasks can be documented
by finding the red safety latches on the right door in the unsecured position. He did not have firm habits in conducting pre-flight preparation, pre-flight procedures as specified in the flight manual, and the aviation regulations requirements. The pilot may not have been recording the actual fuel quantity in the Flybox Mini EIS or, in this instance, may have done so incorrectly. The instrument data record showed a value of 20 litres of fuel prior to the first flight on the day of the air accident. He set the value indicating the fuel amount at 30 litres before taking off from the precautionary landing point in the field, thus the testimony of the service organisation’s technician has been confirmed.
Pilot’s response to unusual situation
The pilot responded in an inappropriate and unsafe manner to an unusual situation, which was, most likely, the left door opening during flight and causing an extreme increase of the noise in the cabin. By letting go of the collective control lever and concentrating on closing the passenger side door, he lost control of the UL helicopter, which went into an extremely sharp descent with a rightward rotation when the main rotor and engine power parameters suddenly changed. Although the pilot realised his error after approximately 3 seconds and attempted to correct the unusual position by intervening in the controls, he was unable to prevent the impact with the ground.
Flight Performance
The pilot did not perform important steps before engine start in accordance with the flight manual. He failed to enter the actual true fuel quantity into the Flybox Mini EIS. He failed to physically check the left passenger side door for secure closure before the take-off from the precautionary landing point and may have been content with the extent of “secured position” of the red door latches (see Figure 19). The pilot performed a flight with a UL helicopter without valid statutory insurance, a take-off weight exceeding the maximum take-off weight by approximately 50 kg and a without the secondary radar transponder on.
The critical situation occurred 50 sec after take-off in the climb phase at a vertical speed of 2 m∙s-1 when the UL helicopter was approximately 100 m above the ground. At the moment when the UL helicopter reached a GPS speed of 65 kt, due to aerodynamic forces, the improperly closed left door opened, which resulted in an extreme increase of noise inside the cabin. The pilot immediately attempted to close the door, presumably with his left hand. In order to be able to do so, he let go of the collective control lever and leaned as far forward and to the left as possible over the passenger to reach the handle of the left door closing mechanism. The collective control lever moved to the lower position spontaneously, but probably also due to pressure from the passenger’s right leg, significantly reducing engine power and causing the UL helicopter to transition from climb to descent in autorotation. The forward movement of the pilot’s body affected the position of the centre of gravity and also inadvertently depressed the cyclic control lever forward. Both these actions combined affected adversely the main rotor, which lost thrust and went into low “G” mode. The UL helicopter pitched nose down towards the ground and made several right turns about the longitudinal axis in a steep descent. The pilot apparently attempted to recover the UL helicopter from the abnormal flight mode but was unable to prevent an impact with the ground.
Conclusions/Causes
The cause of the air accident was an unreasonable reaction to an unusual flight
situation – the spontaneous opening of the improperly closed left cabin door of the UL helicopter shortly after take-off. The subsequent loss of control caused the UL helicopter to enter a steep descent and impact into the ground.
Safety Recommendations
Taking into account the information that not all operators/owners of the UL helicopter CH 77 Ranabot are willing to invest financial resources in the installation of a device to check and indicate the correct secure closing of the door (warning light doors inspection), the AAII issues safety recommendation CZ-22-001.
Safety Recommendation CZ-22-001
The AAII recommends that the Light Aircraft Association of the Czech Republic consider the process of extending the validity of the technical licenses only for UL CH 77 Ranabot helicopters registered with the LAA of the Czech Republic with the installation of a warning light doors inspection in accordance with Service Bulletin SB-70.
Attached final report in PDF file is in original Czech language.