A pilot's incomplete readback led to a PA-44 Seminole overtaking a C172 in the Jandakot circuit in June, according to the ATSB report released last week.
A solo student pilot was returning to Jandakot in Seminole VH-KZJ from a navex at the same time a pilot in C172 VH-ZER was coming back from the training area.
Local procedures require aircraft to contact Tower at specified approach points (in this instance Oakford and Russell) then track to Forrestdale Lake. From there, aircraft were to fly overhead the airport at 1500 AMSL towards the north and join the circuit as directed.
After both had passed Forrestdale Lake and were tracking parallel, Jandakot Tower instructed the pilot of the Seminole to overtake the C172 as they approached the circuit area. That failed to happen, so the tower ATC amended their instruction to the Seminole pilot to "follow the Cessna" and instructed the C172 pilot to join downwind and land first.
However, the pilot of the Seminole continued to overtake the C172, turning inside it on the downwind turn and landing first.
“The Seminole pilot did not identify this final part of the amended instruction, likely due to receiving an unexpected cockpit traffic alert at the time the approach clearance was issued,” ATSB Director of Transport Safety Stuart Macleod said.
“Consequently, the Seminole passed the Cessna as per the original clearance, reducing separation between the two aircraft.”
ATSB investigators found that the Seminole pilot did not readback the "follow" instruction in the revised approach clearance.
“This was not corrected by the controller as the Manual of Air Traffic Services [MATS] did not explicitly require sequencing instructions to be read back,” Macleod said.
The ATSB issued Airservices Australia with a Safety Issue, stating: "The [MATS] did not explicitly state that sequencing instructions were required to be read back by a pilot, providing no assurance that this safety-critical aspect had been correctly understood."
Airservices has responded saying they are reviewing the MATS and AIP to investigate changes to include a "follow" instruction in a clearance readback.
The full report is on the ATSB website.