High ‘collision risk’ as planes were 50ft apart

Two aircraft came within 50 feet of each other over Perth, an official report has revealed. The probe said “safety had not been assured and that a risk of collision had existed”.

One of the two planes put the separation as close as 50ft vertically and just 33 ft horizontally.

The incident, which happened on December 17, was given the UK Airprox Board’s second highest collision risk rating.

The pilot of a Cessna 152 said that they were completing a final circuit on a flying instructors’ course.

They were approaching the downwind leg position when a PS-28 cruiser light aircraft was spotted by the flight instructor 10m away and 50ft below. There was insufficient time to react and take avoiding action. The pilot assessed the risk of collision as “high”.

The PS-28 pilot said they believe they made two errors. First, they did not leave sufficient space from the plane in front of them before commencing their take-off roll.

Then, they elected to fly behind and under the C-152 and perform an orbit in order to increase separation. This resulted in poor vertical and horizontal separation because they did not take account of the performance difference between the two aircraft.

The UK Airprox Board – which investigates near misses – agreed the C152 pilot had been aware that the PS-28 had been behind them in the circuit, but had “no specific situational awareness” regarding how close it had been to their aircraft.

Members noted that neither aircraft had been fitted with any additional form of “electronic conspicuity equipment”, and considered that, had the C152 been so equipped, this may have assisted its pilot in gaining sufficiently accurate situational awareness.

They would have then been able to manoeuvre to increase separation from the PS-28 before sighting it.

“Members agreed that the catalyst for this Airprox had been that the PS-28 pilot had not left sufficient time (and therefore distance) between the C152’s take-off ahead of them and their own departure, noting that the PS-28 pilot had identified this themselves at the time,” said the board.

“Members felt that the PS-28 pilot may have misjudged the climb-rate of the C152 – which had two occupants – compared to their own aircraft with only one occupant which had probably exacerbated the potential for the PS-28 to catch up with the C152.

“Notwithstanding, the board agreed that it had been for the PS-28 pilot to integrate with the pattern formed by the C152.

“Finally, the board considered the risk involved in this Airprox. Members noted that the C152 pilot had been unsighted on the PS-28 until it had been too late for them to take any effective action to increase separation, but that the PS-28 pilot had been visual with the C-152 as they tried to integrate into the circuit behind it.

“Although there had been no GPS or radar data for the C152 available to the board, members noted that both pilots had assessed there to be very little lateral separation, although their assessments of vertical separation differed by 150ft. Members considered that directly under-flying another aircraft should be avoided because any unpredicted change in altitude of the aircraft being under-flown will present a higher risk to the under-flying aircraft.

“The board agreed that safety had not been assured and that a risk of collision had existed. Accordingly, the board assigned a Risk Category B to this incident.”