Near collision due to runway incursion involving Van's RV-7, VH-VTZ and Glaser-Dirks DG-400 motor-glider, VH-XJZ, at Gympie ALA, Queensland, on 27 August 2016

What happened

On the morning of 27 August 2016, a Van’s RV-7 aircraft, registered VH-VTZ, and a Glaser-Dirks DG-400 motor-glider, registered VH-XJZ, were both prepared for flight from Gympie aircraft landing area (ALA), Queensland.

The pilot taxied the motor-glider from the Gympie ALA glider hangars and back-tracked on the grass alongside runway 14 (Figure 1). Before entering the runway strip, the pilot made a radio broadcast on the common traffic advisory frequency (CTAF) 126.7, that they were entering and back-tracking runway 14. On arrival at the runway threshold, the pilot made another broadcast that they were lining-up on runway 14. The pilot taxied the motor-glider onto the threshold of runway 14 and conducted their engine run-up checks. After about 10–15 seconds, they made a broadcast that they were rolling on runway 14 and released the brakes for take-off.

At about the same time as the motor-glider was backtracking runway 14, the pilot of the RV-7 made a broadcast on the CTAF that they were taxiing from the general aviation hangars. At the runway holding-point, the pilot then made a broadcast that they were entering and back-tracking runway 14 (Figure 1). Neither pilot heard the broadcasts from the other pilot.

The motor-glider started the take-off roll from the threshold of runway 14 and as it approached take-off speed, the pilot noticed the top of another aircraft (RV-7) appear on the horizon. Both pilots applied their aircraft brakes and veered to their right. The aircraft came to a stop next to each other on the runway abeam the glider hangars at about 1110 Eastern Standard Time (EST). The pilots performed a radio check and verified they could hear each other and both were broadcasting on the CTAF 126.7. They then proceeded on their planned flights without further incident.

Gympie runway slope

From the runway 14 threshold, runway 14 slopes upward to a crest, which is in line with the glider hangars (Figure 1). Runway 14 then slopes downhill to the threshold of runway 32. The motor-glider pilot commented that in an aircraft low to the ground, such as a glider, stationed at the threshold of runway 14, the pilot would not be able to see an aircraft such as the RV-7, back-tracking runway 14, until the other aircraft was abeam the glider hangars (Figure 1). The RV-7 pilot commented that when back-tracking runway 14 in their aircraft they cannot see another low profile aircraft, such as a glider, until they are about 300 m from the threshold of runway 14.

Aircraft radios

The RV-7 has one radio antenna located on the underside of the aircraft. The motor-glider pilot was unsure of the location of their radio antenna, because they are integral to the airframe in order to minimise drag. Both aircraft radio systems are capable of monitoring two frequencies, but can only broadcast on one. Both pilots confirmed they had 126.7 CTAF set and in use as their active frequency at the time of the serious incident. However, the RV-7 pilot commented that their radio microphone may not have been up against their mouth, which would have reduced the volume of their transmissions.

Figure 1: Gympie ALA and ground tracks of the aircraft

Source: Google earth, annotated by ATSB

Previous incidents

Both pilots commented that there have been previous incidents of traffic conflicts between aircraft, which started with missed radio calls when the aircraft were at opposite ends of the main runway (runway 14/32). On these previous occasions, aircraft airborne in the circuit could hear the radio calls of opposite end traffic on CTAF, despite the traffic on the ground not hearing each other.

A search of the ATSB notifications database indicated that in 2016 there were two incidents at Gympie ALA, where the reporter has indicated that a broadcast was either not made, or not heard. It is unknown if terrain shielding contributed to these events.

ATSB comment

The ATSB notes that it is reported that traffic at Gympie ALA is increasing and therefore exposure to the risk presented in this report is increasing. Despite the fact that both pilots made all the required radio calls for their planned operation, a runway conflict occurred. There is currently no reference to the potential for terrain shielding of radio calls in the Gympie ALA Enroute Supplement Australia entry.

Safety action

Whether or not the ATSB identifies safety issues in the course of an investigation, relevant organisations may proactively initiate safety action in order to reduce their safety risk. The ATSB has been advised of the following proactive safety action in response to this occurrence.

RV-7 pilot

As a result of this occurrence, the pilot of the RV-7 has advised the ATSB that they are taking the following safety action:

Radio checks

The pilot of the RV-7 indicated they would introduce a radio check broadcast, when circumstances permit, during their start checks to verify their transmission volume and readability.

Aerodrome Operator

As a result of this occurrence, the Gympie Aerodrome Operator has advised the ATSB that they are taking the following safety action:

Enroute Supplement Australia

The Gympie Aerodrome Operator indicated they intend to add a note to the Gympie entry in the Enroute Supplement Australia, under ‘Additional Information’, to advise pilots that poor radio propagation between aircraft operating on the ground at opposite ends of the main runway may be experienced.

Safety message

A potential accident was avoided by the actions of both pilots who responded to the presence of the other aircraft by braking and veering to the right. Rather than continuing their flights with the assumption the other made a mistake, they performed a radio check with each other to verify there was no fault with their respective aircraft radios.

Aviation Short Investigations Bulletin - Issue 54