Two Training Aircraft Nearly Collide Near Wonderboom

Casualties unknown • FAD 127 Wonderboom General flying Area, ZA

A mid-air near-miss involving two Cessna 172P aircraft occurred during flight training exercises in a South African danger flying area.

What happened

On the afternoon of 10 May 2021, two separate training flights involving Cessna 172P aircraft experienced a close proximity incident within the FAD 127 Danger Flying Area. The first aircraft, ZS-GDA, departed Wonderboom National Aerodrome at 1333Z for stall training exercises, climbing to 7,000 feet.

Approximately twenty minutes later, a second Cessuna 172P, registration ZS-PMX, departed the same aerodrome for similar training purposes. Radar tracking indicated that ZS-PMX performed several turns within the flying area. At approximately 14:08Z, radar data showed that the two aircraft came dangerously close to one another. While the pilot of ZS-GDA observed the other aircraft and attempted to communicate via radio, the aircrafts' paths intersected at a point where altitude separation was not clearly established by radar.

The investigation

SACAA AIID examined the flight paths and communication logs of both aircraft. The investigation noted that while the aircraft were using the correct VHF frequency (124.40 MHz) for the area, the crew of ZS-PMX experienced initial difficulties with radio audibility on their primary frequency, eventually switching to a secondary radio.

Investigators also found that the transponder on ZS-PMX was not providing Mode C altitude information to air traffic control, meaning the height of the aircraft could not be monitored by radar. Furthermore, neither aircraft had filed a flight plan prior to departure, which prevented the assignment of specific squawk codes for better radar identification.

Findings

  • The investigation found no evidence of any avoidance maneuvers being performed by either crew during the encounter.
  • A primary contributing factor was the failure of the ZS-PMX aircraft to correctly utilize the appropriate radio frequency upon entering the general flying area, which likely prevented the crew from being heard by other traffic.
  • The lack of Mode C functionality on ZS-PMX prevented air traffic control from determining the aircraft's altitude.
  • The absence of filed flight plans for both aircraft hindered effective radar tracking and identification.

Probable cause

The near-miss was likely caused by the ZS-PMX crew failing to establish effective communication on the correct frequency, combined with a lack of altitude information due to non-functional Mode C transponder data.

Frequently asked questions

What happened in the 2021-05-10 Cessna 172 P (Both) accident near FAD 127 Wonderboom General flying Area, ZA?

A mid-air near-miss involving two Cessna 172P aircraft occurred during flight training exercises in a South African danger flying area.

What aircraft was involved and where did it happen?

The accident on 2021-05-10 involved a Cessna 172 P (Both), registration ZS-GDA and ZS-PMX, at FAD 127 Wonderboom General flying Area, ZA.

What was the probable cause of the accident?

The near-miss was likely caused by the ZS-PMX crew failing to establish effective communication on the correct frequency, combined with a lack of altitude information due to non-functional Mode C transponder data.

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