On 8 December 2013, the pilot in command of a Pitts S2-B equipped with a Lycoming AEIO-
540 engine and Hartzell two-blade metal propeller, took off for an aerobatic flight during
which he performed several figures leading to a rapid variation in the orientation of the
axis of rotation of the propeller.
Returning from the flight, in the downwind leg, the pilot felt vibrations which increased
in intensity. He reduced engine power and declared an emergency. The assembly formed
by the propeller and part of the crankshaft separated from the engine and struck the fin.
Observing the appearance of smoke and the presence of oil on the windshield of the
aeroplane, the pilot shut down the engine and performed a forced landing.
The accident resulted from progressive fatigue cracking and then the rupture of the
crankshaft due to the propeller applying rotational bending loads to the crankshaft during
certain aerobatic manoeuvres. The investigation showed that the combination of Lycoming
AEIO-540 engines and Hartzell two-blade metal propellers, when used in aerobatic flights
comprising certain manoeuvres with a strong gyroscopic effect, constituted a higher risk
factor of crankshaft rupture.
In 1988, the engine manufacturer, Lycoming, issued a Service Bulletin (SB) recommending
a visual inspection of all the crankshaft area situated between the oil seal and propeller
flange. This inspection, which must take place every ten hours of aerobatic flight including
figures in the “unlimited” category, requires the removal of the propeller, starter ring gear
and oil seal. The complexity, frequent repetition and time required to carry out the tasks
specified by this SB make its application restrictive and the operators taking it into account
This SB did not give rise to the publication of an Airworthiness Directive (AD) by the FAA,
primary certification authority of the aeroplane, engine and propeller. The Australian
and New Zealand civil aviation authorities imposed compliance with this SB by issuing
an Airworthiness Directive. The BEA has recorded several accidents similar to that to the
F-GEAL, concerning aerobatic aeroplanes equipped with a Lycoming engine and twoblade
metal propellers. It is probable that their operators were not aware of this SB. The
inspection specified by this SB was not carried out on F-GEAL.
On the basis of the safety investigation, the BEA has sent two safety recommendations to
the FAA and one to EASA concerning aeroplanes equipped with the engines concerned by
the given SB and Hartzell two-blade metal propellers.
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