Airprox Report 2013086

3
Three other aircraft are shown: a B747, 38.2nm West of the A320 at FL370 tracking east-
southeast; a B737, 23.4nm northwest of the A320 at FL358 tracking south-southeast and
another B737, 28.2nm ahead of the A320 at the same level on a similar routeing.
The NATS Ltd AIS pre-flight bulletin, nav-warning for the London FIR, contained three
NOTAMS which promulgated the release of Meteorological and Radiosonde balloons (with
unlimited upper levels). The sponsors of each were contacted and it was confirmed that no
balloons were released from the specified sites on the incident date.
A NATS Ltd investigation was not able to verify the origin, level or size of the object reported
by the A320 pilot. The Military Radar Analysis Cell (RAC) where unable to trace the reported
object.
There were no radar traffic returns within the immediate vicinity of the A320. There were two
aircraft 20nm and 35nm West and slightly above the level of the A320 and one aircraft 20
miles ahead of the A320 at the same level. It was considered possible that given the position
of the sun, these aircraft may have been glinting in the sun. However, it was not possible to
trace the object or determine the likely cause of the sighting.
Summary
An A320 pilot, in Northbound level cruise at FL340, perceived an object through the LH DV window
which he assessed as travelling towards him at the same level, slightly above the flight deck
windscreen. There were no aircraft in the vicinity indicated on TCAS or on radar. There were no
recorded releases of meteorological balloons in the area.
PART B: SUMMARY OF THE BOARD'S DISCUSSIONS
Information available included a report from the A320 pilot, radar video recordings and a report from
the appropriate ATC authority.
The Board established that there did not appear to be any conflicting traffic on radar and that no
TCAS alerts or advisories had been issued. The involvement of a meteorological balloon was ruled
out and it was calculated that a helium filled envelope would have to be of the order of 1m in diameter
to reach FL340, hence ruling out commercially available toy balloons. Nevertheless, the A320 pilot
was subject to a powerful impression of immediate danger, caused by his perception of an object
closing rapidly on his aircraft. Although only supposition, members opined that this may have been
due to a combination of a possible reflection from the low sun off one of the aircraft to the West, and
of the pilot’s head movement as he looked forward. After some discussion it was decided that,
although the reflection theory held some merit, the overall dearth of information relating to the event
rendered a meaningful finding impossible.
PART C: ASSESSMENT OF CAUSE AND RISK
Cause: Sighting report.
Degree of Risk: D.
ERC Score4: N/S
4 Although the Event Risk Classification (ERC) trial had been formally terminated for future development at the time of the
Board, for data continuity and consistency purposes, Director UKAB and the UKAB Secretariat provided a shadow
assessment of ERC.