Accident to Europa G-KWIP, 12 March '00. (my own assessment of evidence)
Dave & I would like to share our understanding of what went wrong on 12th
March 2000 in the hope that by doing so we might help to avoid a repeat of
this accident.
The coolant in this aircraft had been diluted to approximately 60/40
glycol/water in line with Europa and Rotax thinking. The aircraft had a
modified cooling system similar to early experiments in the development of
the Europa XS. It had operated for more than 2 years without problem in
that configuration. A cold air box for carburetor air was not fitted at the
time.
On the accident day the aircraft had stopped, engine running, at the runway
threshold for about 10 minutes, probably adjusting EFIS system parameters
so that the engine would have been quite warm. About 20 seconds after the
start of take off, at 50 to 60 feet above ground, white vapour was seen to
exit the cowling and the engine was heard to lose power. The aircraft
started a gentle turn, to avoid trees and buildings? then abruptly departed
and struck the ground almost vertically from an estimated height of 100 feet
The Air Accident Investigation team found traces of coolant in all four
cylinders and the coolant collector bottle had burst. A joint in the
radiator hose had also apparently separated. Whether this latter occurred
in flight, on impact or even during movement of the aircraft afterwards was
never ascertained. The suspect radiator hose joint had been subjected to a
lot of radiant heat from the exhaust downpipe at the rear of the engine,
which would have caused softening of the hose which is only rated to take
110 degrees C and 2 bar pressure. With pressure up to 5 bar and temperature
at least 130 deg C the clamping pressure would have been reduced due to
extrusion of the rubber. There was an extra hose joint at this point on G-KWIP.
Subsequent pressure testing of a new Rotax coolant collector bottle, at 90
degrees C resulted in bursting of the bottle at about 5 bar, 70 lbs/sq. in.
This temperature was chosen to represent the lowest possible burst
pressure. Higher temperature would result in severe inflation, which did
not occur on G-KWIP although after the accident the bottle might have
relaxed to a lesser volume. It is almost certain that the cowling had
filled with coolant vapour and caused significant loss of power, 18 gms of
water produces 22.4 liters of vapour. When the collector bottle burst,
coolant, if not already boiling would have hit the red hot exhaust pipe
adding to the volume of vapour. Almost certainly coolant would have spread
over the windscreen as it did in a subsequent incident in a USA Europa XS,
adding considerably to the already high workload.
50/50 glycol water boils at around 130 degrees C at 1 bar overpressure, and
only
110 degrees at ambient pressure, well below the max allowed CHT (150 deg).
Our suggestions in the light of 20/20 hindsight:
Coolant be maintain to at least 80% glycol.
Adequate overboard overflow provision for the collector bottle.
Cold air box for the carburetor intakes to prevent ingestion of in cowling
vapours,
Incorporation of any one of these criteria would probably have prevented the
accident, as would our leaders' insistence "Fly the Airplane!" and if
necessary
accept a controlled crash. (Burt, Mike Melville and Ivan) A stall warner
would perhaps have helped too, at a time of very high workload.
Graham Singleton
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