Recommendation

SUBJECT



Unsafe circuit procedures at airfields with considerable glider
activity.



OCCURRENCE SUMMARY



Immediately after release from a tug aircraft, a two-seat glider
commenced circling in the circuit area at Tocumwal at about 2,000
ft above ground level . At the same time, a high performance
single-seat glider approached the circuit at high speed from the
north-west, pulled up and collided with the circling glider. Both
aircraft were severely damaged by the collision and subsequent
ground impact, and all three occupants were fatally injured.



SAFETY DEFICIENCY



There were no procedures in place for the use of radio in the
circuit area although both aircraft were equipped with VHF radios
tuned to the Common Traffic Advisory Frequency (CTAF).



There were no procedures in place to prevent gliders entering the
circuit area at high speed in an area where other gliders were
manoeuvring at slow speed.



Neither glider involved in this accident were painted with
high-visibility markings even though gliders can be particularly
difficult to see in the air.



ANALYSIS



Similar accidents investigated by the Bureau of Air Safety
Investigation:



Four fatal mid-air collisions that involved at least one glider
have occurred since 1990, in or near the circuit area of airfields
where considerable gliding activity was taking place:

Tocumwal NSW, 2 November 1990, mid-air collision
VH-CAG/VH-GXO;

Tocumwal NSW, 8 February 1992, mid-air collision
VH-UKT/VH-GQR;

Jondaryan Qld, 1 November 1992, mid-air collision
VH-SCT/VH-WQR;

Benalla Vic, 24 November 1993, mid-air collision
VH-AYB/VH-GMN.



Including the latest accident at Tocumwal, a total of eight
fatalities have resulted from these five accidents.



A procedure for the use of radio to broadcast position and
intentions near the circuit area would have lessened the risk of
collision.



The Gliding Federation of Australia (GFA) produces a handbook for
glider pilots (Airways and Radio Procedures for Glider Pilots),
which mentions the use of radios in a CTAF but does not
specifically recommend a circuit entry call (see attachment
1).



Recommendations have been made by various state coroners regarding
the use of radios near the circuit area to minimise the risk of
collision.



The coroner who carried out the inquest into the midair collision
at Tocumwal on 8 Feb 1992 recommended that a Mandatory Traffic
Advisory Frequency (MTAF) be established for the purpose of pilot
to pilot communication within the traffic area. He believed that if
the glider pilot had been required to broadcast his intention to
modify his circuit on the gliding frequency, the pilot of the tug
involved in the collision would have heard this transmission. He
also believed that in those circumstances, it is unlikely that the
accident would have happened (see attachment 2).



As the limitations of unalerted see-and-avoid to prevent
collisions are well known, better use of radios now fitted to most
gliders would reduce the risk of collision near the circuit areas
of busy gliding airfields. Although powered aircraft also operate
into CTAFs where there is gliding activity, they are normally
easier to see than gliders, especially from directly in front or
behind. Powered aircraft normally fly a more predictable circuit
pattern and are less affected by weather conditions in the circuit
area. Because of the variable height and speed of gliders in the
circuit area, they are considered to pose a higher collision risk
than powered aircraft.



Due to the variable speed and tracking involved in glider flying,
the requirements for the use of radio in CTAFs, as covered in AIP
OPS NCTL-14 (see attachment 3), do not provide sufficient
protection from collision. The very large CTAF at Tocumwal (15 NM
radius) could result in gliders operating for considerable time
away from the circuit but still within the CTAF and therefore not
required to make a CTAF entry radio call. On the day of the most
recent midair collision at Tocumwal, no calls were heard from the
pilot of the high-performance single-seat glider during his last
flight of over 6 hours. In addition, CTAF areas where there is
considerable gliding activity vary in size from the standard 5 NM
radius with some at 10 NM and Tocumwal at 15 NM radius. Because of
the differences in dimensions of the CTAFs, the time between the
CTAF entry call and circuit entry depends on the airfield. A
circuit entry call at 3 NM miles would remove any possible
confusion as to the distance a glider is from the field.



The pilot of the glider that approached Tocumwal airfield at high
speed on 5 January 1997 was probably practising a competition
manoeuvre called a "final glide". A final glide is used during
competition to achieve the shortest possible time over the last
sector and ends with the glider passing over the timing point on
the airfield at low level and high speed. The pilot then rapidly
climbs the glider, reduces its speed and positions it in the
circuit for landing. While these manoeuvres are expected during a
competition, it is unsafe to have gliders that are difficult to see
entering an area at high speed when they are not expected,
especially if they are performing sudden pull-ups where other
aircraft are circling. Modern high-performance gliders have
never-exceed speeds (Vne) of over 140 kts and may operate close to
Vne during a final glide. Normal circling and circuit speeds are
between 45 kts and 65 kts.



Gliders are designed with minimum frontal area to reduce drag and
the frontal area of modern high-performance gliders is very small,
with the pilot in a semi-reclined seating position, making them
especially difficult to see from the front. Most composite gliders
are coloured white, giving poor contrast against clouds or hazy
sky. Most older metal gliders are unpainted and the bare aluminium
finish is reportedly difficult to see against a clear blue sky. The
adoption of high-visibility markings may assist pilots in seeing
another glider in time to avoid a collision.



Following discussions with BASI, both the Gliding Federation of
Australia and the Sports Aviation section of CASA agree that some
protection is necessary near busy circuit areas and that a speed
limit and radio advisory call should improve safety. Although radio
use in gliders is not mandatory in CTAF type operations, some
countries in Europe require a pilot to hold a formal radio
operator's licence before they can undertake a cross-country glider
flight. The GFA is considering introducing similar radio
qualifications in Australia.



REFERENCES



1. Gliding Federation of Australia, Airways and radio Procedures
for Glider Pilots, March 1996.



2. Document:"Inquest Before Coroner Sitting Alone concerning the
death of Alan Leslie Whitely", dated 26 November 1992.



3. AIP OPS NCTL-14, paragraph 4, issued 7 December 1995.