Accident Arsi VM-1C Esqual OO-H78,
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ASN Wikibase Occurrence # 201533
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Date:Sunday 19 November 2017
Time:16:12 UTC
Type:Silhouette image of generic VM1 model; specific model in this crash may look slightly different    
Arsi VM-1C Esqual
Registration: OO-H78
MSN: SE006
Fatalities:Fatalities: 0 / Occupants: 2
Aircraft damage: Substantial
Location:Landegem, East Flanders -   Belgium
Phase: En route
Departure airport:Ursel Airfield (EBUL)
Destination airport:Ursel Airfield (EBUL)
Investigating agency: AAIU
Confidence Rating: Accident investigation report completed and information captured
The plane was flying southwest of Gent, Belgium, when a propellor failure occurred. The crew managed to land the plane safely in a field close to Landegem.

The aircraft was being test flown after a new propeller had been fitted. The importer and the owner agreed to perform flight tests together, in order to determine the optimum blade pitch angle.
The importer was at the controls and acted as pilot in command (PIC) and select different power settings. The owner sat in the left-hand seat to record the aircraft parameters.
The aircraft took off from the EBUL airfield at 15:49. About 19 minutes later, just after flying above the west side of the city of Gent, the aeroplane was in a descent with a TAS of 215 km/h and an engine power setting of 2800 RPM, passing
2200 ft AGL when suddenly the occupants felt a light vibration. The PIC reduced the power somewhat and the vibration disappeared. But immediately after, the occupants heard a loud bang and the aeroplane experienced heavy vibrations that shook the whole aircraft. The engine stopped abruptly and the vibrations ended.
The PIC noticed that the engine cowl seemed loosened and at the same time a sort of mist entered the cockpit. The first impression of the PIC was that the aeroplane had collided with something. The PIC’s first action was to check if the aeroplane still responded normally. He noticed that the engine was stopped and did not see any propeller blade. The owner however, still saw one propeller blade on the left side of the engine cowl. The crew then realized the propeller had lost one of the two blades.
The PIC had no choice but to land the aircraft in emergency. He tried to send a mayday, but noticed that the radio was not working. Therefore, the owner sent a SMS text message to the EBUL airfield for warning them about the emergency landing. During the approach, the PIC checked whether the electrical flaps were still operating and shortly before touchdown, selected full flaps. The aeroplane touched down at a ground speed of 65 km/h on a wheat field and rolled over a distance of 45-50 m. The gliding phase lasted about 4 minutes.
The aeroplane did not suffer additional damage further to the emergency landing and both occupants climbed out uninjured. The lost propeller blade was found in a hedge the day after.

Findings as to causes and contributing factors
- The investigation determined that the in-flight separation of one blade of the propeller was due to low cycle/high stress fatigue at the blade root. [direct cause]
- The investigation could not determine the exact origin of the fatigue. The ruptured blade did not show sign of accidental damage that occurred prior to the event, nor did the owner indicate that any incident occurred that was likely to weaken the concerned blade. It is therefore likely, given the fact the failed during a test flight after having run only 1h26 (ground checks included) that the origin of the fatigue at the blade root was caused by vibrations originating from the engine/propeller combination.
- The two blades are installed on the propeller hub and the blade angle is set manually. Any unbalance between the angle of both propeller blade and tightness of fixation is susceptible to generate vibrations. The investigation could not identify whether such condition existed prior to the event.
- The analysis of recorded engine parameters showed air pressure fluctuations inside the air filter box at high RPM. The investigation could not determine the cause of this phenomenon and whether the engine could have generated some abnormal vibrations susceptible to damage the propeller [direct cause]
- Test-flight with a new engine/propeller combination was performed without having first reasonably verified that they are compatible, amongst others through the performance of endurance tests on a test bench [indirect cause]
- The airframe manufacturer entrusted the importer to develop a major modification without insuring that he had sufficient technical background and knowledge to cope with all the aspects of such a modification. [contributing factor]
- Neither caution statement nor guidance material exists from both the engine and the propeller manufacturers to assess the compatibility of the engine with the propeller. [contributing factor]

Accident investigation:
Investigating agency: AAIU
Report number: 
Status: Investigation completed
Download report: Final report


Revision history:

21-Nov-2017 07:18 mgossye Added
21-Nov-2017 15:20 Geno Updated [Cn, Location, Source]
16-Feb-2018 07:16 Masen63 Updated [Aircraft type, Source]
14-Apr-2021 07:33 harro Updated [Nature, Departure airport, Destination airport, Damage, Narrative, Accident report]
14-Apr-2021 07:43 harro Updated [Time, Source]
26-Jun-2022 21:21 Ron Averes Updated [Location, Departure airport, Destination airport]

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