The ATSB has issued a safety advisory notice urging pilots to switch on their mode S transponder from engine start, after a Dash 8 entered Wagga Wagga’s main runway while a Piper Cherokee was taking off last year.
On 15 July 2024, a QantasLink Dash 8 twin turboprop was being repositioned from one bay to another at Wagga Wagga Airport, requiring it be turned around by taxiing to the western end of the main runway, backtracking up the runway, and then exiting to return to the apron.
While the QantasLink flight crew was preparing for the repositioning, a Piper PA-28 light aircraft, operated by the Australian Airline Pilot Academy (AAPA), left the apron and began to taxi to the eastern end of the runway for a training flight.
About 10 minutes later, the Piper began its take-off roll from the eastern end of the runway, and the Dash 8 entered the runway at its western end.
The Dash 8 crew was not aware of the Piper until the Dash 8 crossed onto the runway from the holding point, and was notified of the potential conflict by the crew of a third aircraft.
The crew of the Dash 8 used reverse thrust to move back off the runway. At about the same time, the student pilot in the Piper rejected their take-off, and taxied off the runway mid-runway.
The ATSB’s investigation identified several factors that contributed to the Dash 8 crew not being aware of the Piper before entering the runway, including:
- The reduced strength of ground-based VHF radio calls at the eastern end of the runway and the parallel taxiway, where the Piper was located.
- The Dash 8 crew making and receiving ground-based transmissions on the aircraft’s VHF COM 2, as per QantasLink procedures. The location of the VHF COM 2 antenna on the belly of the aircraft likely led to situations where other aircraft had difficulty receiving and understanding radio transmissions, and where the Dash 8 did not receive the Piper’s radio transmissions.
- The Piper pilot making the recommended radio calls but not attempting to directly communicate with the Dash 8 crew to arrange separation.
- The crew of the Piper not switching on the aircraft’s mode S transponder during taxi.
Unalerted to the presence of the Piper, the Dash 8 crew did not visually detect it at the other end of the runway, about 1,700 m away.
Acknowledging a series of factors had contributed to the occurrence, ATSB Chief Commissioner Angus Mitchell noted the Piper’s mode S transponder, if switched on, likely would have made the smaller aircraft conspicuous on the Dash 8 crew’s electronic flight bags.
“AAPA’s operating manual only required pilots to activate the transponder prior to entering the runway,” Mr Mitchell noted.
“The use of a mode S transponder during taxi would normally provide an additional source of positional data to other pilots, aiding visual identification and alerted ‘see-and-avoid’ to other aircraft.”
In response, AAPA has changed its PA-28 Flight Crew Operating Manual, and Quick Reference Handbook, instructing that the transponder be selected to ALT mode after engine start.
More broadly, the ATSB has issued a safety advisory notice to all pilots and aircraft operators to follow suit and review their own procedures, and encourages all pilots to ensure mode S transponders are on from the first movement of the aircraft on the ground, particularly at non‑controlled aerodromes.
“Using the mode S transponder with ADS-B OUT enabled is the most effective way to make an aircraft electronically conspicuous for other aircraft, as well as the ground air traffic management environment,” Mr Mitchell said.
The ATSB’s final report also notes the use of the Dash 8’s belly-mounted VHF COM 2 antenna, as opposed to the roof-mounted VHF COM 1 antenna, was also identified as a likely contributing factor in two other ground communication events at Mildura Airport (AO-2023-025 and AO-2023-050).
“Testing conducted during the latter of those two investigations identified reception and transmission on the lower antenna on the ground had significantly reduced strength and clarity compared to the upper antenna,” Mr Mitchell said.
Aligned to this, De Havilland Aircraft of Canada Limited has also advised the Dash 8’s VHF COM 1 may provide a better line of sight with other aircraft or ground stations possibly resulting in improved communications for both transmission and reception.
The Civil Aviation Safety Authority also released new guidance and recommendations relating to the use of radios where the antenna is mounted on the underside of the aircraft fuselage to both Advisory Circular (AC) 91-10 and AC 91-14.
QantasLink has advised the ATSB that further assessment of the use of VHF COM 1 for ground-based communications at non‑controlled aerodromes for Dash 8 aircraft is being assessed, but is not yet finalised.
“The ATSB will monitor this safety issue as this action progresses,” Mr Mitchell said.
Read the final report: Runway incursion involving De Havilland Aircraft of Canada Limited DHC‑8, VH-QOD, and Piper PA-28, VH‑XDK, Wagga Wagga Airport, New South Wales, on 15 July 2024