The ASI should be connected to a fuselage static, but
in the case of the accident glider it was connected
to some sort of double pronged European Total energy
(TE) probe in parallel with the varios.

T.E. probes produce a small amount of negative pressure
which increases with airspeed and thereby compensates
the vario for the height gains or losses associated
with speed changes. i.e converts it from a Vertical
Speed Indicator to a soaring Vario.

An ASI works by comparing pitot pressure with static
pressure, so reducing the static pressure will as you
say increase the ASI reading. However the glider had
been flown in this configuration for some time, so
the pilot would have been used to any errors produced.
The AAIB actually set up a rig with the same configuration
and found that the errors where quite small. Presumably
the high pressure generated by the pitot was much greater
than the low pressure generated by the TE probe.

If you want to be really pedantic, the shoulder straps
were actually found to be undone and too long after
the accident, but they may have slipped and then released
during the crash. There is however at least a possibility
that the pilot may have failed to secure the shoulder
straps before taking the launch.

As I have also slipped back in the cockpit of a DG
glider when I didn't quite tighten the shoulder straps
enough for a winch launch, this seems the most reasonable
explanation for this accident to me, and doesn't change
the basic recommendations.

Derek Copeland


At 11:06 17 October 2006, Doug Haluza wrote:

Derek Copeland wrote:
The UK Air Accident Investigation Branch (AAIB) has
recently published a report on a fatal accident involving
a DG600 sailplane back in 2005.

The only anomaly found was that the ASI static was
connected to the Total Energy probe, which might have
caused the ASI to misread. However tests showed that
this would only cause minor errors.

This seems completely wrong to me. The TE probe should
produce a
pressure below static equal to the dynamic pressure,
so the
differential pressure to the ASI would be doubled,
and the ASI would
read high by 70%. I would not consider this a minor
error!

I would seriously question the test results, and the
report's
conclusions based on this.