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Zulu Sierra Project

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The accident

On June 7th 2015, the F-BOZS departed, left the ground for a flight lesson during which, in particular, low speed flight was praticed.
After about 40 minutes, the crew completed the exercise and came back to Saint-Cyr airfield for landing.
During base leg, the instructor thought that the aircraft was a bit too low and asked student pilot to increase power in order to come back on the approach profile.
Student pilot performed requested action and tried to increase gradually engine power in order to come back on the approach profile but he didn’t get any reaction from the engine even when full power was applied on the throttle stick.
He informed his instructor of the situation who performed a quick diagnostic and conclude that they were too low to join the airfield.
The instructor tooks control and announced an engine failure on the ATC frequency before trying to land the aircraft into a small INRA (National Institute for Agronomical Research) field located between Saint-Cyr airfield and the Versailles castle.

This location is a group of small experimental field separated by alley, it is a bit rugged and therefore not adapted for landing and rolling a small aircraft.
As the F-BOZS is a tailwheel aircraft, it completed the approach into the field by a bump into one of the alley and then turned upside down (see following picture from the fire rescue departement).



The crew was safe but the instructor, who is a bit tall was more seriously injured than his student pilot due to this rollover.
As we can see on the above picture, fire and rescue departement arrived quickly and deployed substantial efforts in order to bring help to the crew and to avoid any fire breakout.

BEA investigation

Following this accident, BEA (French equivalent of NTSB) started an investigation to find the cause.
This investigation took about a year.
Quickly, human factor were no longer considered and the crew was cleared from any responsibility for the accident.
The investigation then continued and focused on the technical cause that could explain the loss of power encountered by the crew when the problem occurred.
Some deep investigations on the engine and the fuel were performed looking for some elements which could explain the technical failure but without any success.
After a year of investigation, BEA published its report in which it is indicated that the cause of the accident could not be determined (See the link to the report : BEA report).
That’s a big disappointment for the crew and for all flying club’s members that were hoping that BEA would be able to explain what happened that day, but these questions will remain without any answer…

As the BEA report has been published only in French, a translation of this report in English is made below :

Accident of Robin DR221 registered as F-BOZS on 06/07/2015 in Saint-Cyr l’Ecole (78)

1- History of the flight
Back from a local VFR flight of about 40 minutes during which low speed flight has been practiced, student pilot starts his descent at the end of base leg in order to land on runway 29L.
The instructor asks the student pilot to “increase a little bit power” because he thinks that the aircraft is low on the approach plan.
Despite several actions on the thrust lever, the engine rpm doesn’t increase.
Instructor announces to ATC an engine failure. He takes control of the aircraft, check nominal position of engine controls and land into a high cereal field.
During rolling, the aircraft turns upside down.
Firefighters evacuate the crew stuck inside the aircraft.
2- Additional information
The 44 years old pilot, has an instructor rating since December 2013.
He had logged about 1000 hours of flight at the time the event occurred.
3.1- Information on the aircraft and the location
Firefighters has expanded some foam around the aircraft to avoid any fire breakout.
The pressure of the water hoses has compressed the air intake grid and lots of wastes have been pushed into the engine air intake pipe.
These wastes were found in the head of cylinders, from open valves, and also in the carburetor bowl.
Engine and its accessories have been contaminated by mud and organic waste.
Due to this contamination, it has not been possible to determine the origin of inability of the crew to increase engine power.
2.2 Fuel
Collected fuel in the aircraft fuel pump’s bowl looked a bit greenish.
The result of the analysis of this sample indicates that the fuel, of type 100LL, has been polluted by organic elements.
However, the origin of the pollution couldn’t be determined as the container, used to collect and store the sample, wasn’t adapted.
Indeed, it is possible that the container would be the origin of the fuel pollution.
2.3 Estimated weather condition on the crash site
Wind was 10 knots from 290°, temperature was 18°C, dew point was 7°C and relative humidity was 49%.
3- Conclusion
The investigation couldn’t determine the reason for the lack of engine power rise.