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Aviation Safety Advisory A20O0029-D1-A1

200 Promenade du Portage
Place du Centre, 4th floor 
Gatineau, QC K1A 1K8 

30 November 2020

Director General, Civil Aviation
Transport Canada

Re :

Aviation Safety Advisory A20O0029-D1-A1
Inaccurate airborne status transmitted by transponders and its effect on runway monitoring and conflict alert systems

On , at 0948 Eastern Standard Time, an Embraer 190-100 aircraft (registration C-FMZW), operated by Air Canada as flight ACA 1037, with 4 crew members and 83 passengers on board, was conducting a takeoff from Runway 06L at the Toronto/Lester B. Pearson International Airport (CYYZ), Ontario. During the aircraft’s take-off roll, a Boeing 777-300 aircraft (registration C-FJZS), operated by Air Canada as flight ACA 606, with 14 crew members and 345 passengers on board, was instructed to taxi to position and to hold onto Runway 06L. Shortly after, air traffic control issued a take-off clearance to the Boeing 777 while the Embraer 190 was still on the runway.

While still on the take-off roll, the Embraer 190 struck a bird and initiated a rejected takeoff; the aircraft had reached an airspeed of approximately 148 knots. The flight crew made a radio call on the tower frequency that they were aborting the takeoff. At the same time, the Boeing 777 flight crew read back the take-off clearance on the same frequency and commenced their take-off roll. The simultaneous radio transmissions went undetected: neither air traffic control nor the Boeing 777 flight crew heard the Embraer 190 abort radio call.

During its take-off roll, the Boeing 777 flight crew observed that the Embraer 190 was still on the runway and initiated a rejected takeoff; the aircraft reached an airspeed of approximately 134 knots prior coming to a stop on the runway. At this time, both aircraft were on the runway surface separated by approximately 3800 feet. There were no injuries. There was no damage to either aircraft. TSB investigation A20O0029 is ongoing.

The Embraer 190 is equipped with a Honeywell transponder, and a Honeywell Primus Epic integrated avionics system. The Honeywell Primus Epic’s monitor warning function uses software logic that determines the aircraft to be airborne when the aircraft’s indicated airspeed exceeds 50 knots; however, the aircraft may still be on the ground. The result of this determination is used by the transponder for transmitting the aircraft’s airborne status (i.e. air/ground). This transponder configuration exists on all the Embraer E-jets, of which more than 1500 have been produced. Such transponders are also known to be installed on aircraft manufactured by Dassault, Gulfstream, Learjet and Textron Aviation (formerly Cessna).

Many other aircraft manufacturers incorporate other parameters to determine the aircraft’s airborne status. Some may first use a weight-on-wheel parameter and then use speed as a reasonableness check. In some cases, other aircraft will override the weight-on-wheel parameter, and consider the aircraft airborne once the groundspeed is greater than 100 knots. The Primus Epic system does this as well but uses an airspeed threshold of 50 knots, a speed at which becoming airborne is not possible on many of the aircraft equipped with these avionics.

Many air traffic service providers use advanced surface movement guidance and control systems (A‑SMGCSs), which provide controllers with a real-time display of aircraft and vehicle traffic on the airport manoeuvring areas. Runway monitoring and conflict alert (RMCA) systems are a sub-system within the A-SMGCS and are designed to identify, monitor and alert air traffic controllers to possible conflicts and hazards such as runway incursions. RMCAs will typically use surface detection radar and aircraft transponder data to calculate and determine if a conflict exists and then generate an alert if required. Alerts and alarms are intended to prompt controllers to issue alternative instructions to the aircraft or vehicles involved in the hazard. RMCAs are not required airport equipment, but are presently in use at more than 50 major airports worldwide.

The Indra Navia runway incursion monitoring and conflict alert system (RIMCAS) is a type of RMCA. A total of 15 airports, including CYYZ, use a RIMCAS and at least 36 airports in the U.S. use similar systems. The Indra Navia RIMCAS software can be configured to assess various parameters in order to determine the air or ground status of an aircraft.Footnote 1 Since RIMCAS is configurable, it is adapted to the local site and operation in order to minimize false alerts yet maintain a sufficient level of safety and advance warning.

At the time of the occurrence, the Indra Navia RIMCAS used at CYYZ was configured to use data from the aircraft’s transponder transmission as the primary indication that an aircraft had become airborne. In keeping with this, when the Embraer 190’s airspeed exceeded 50 knots on the departure roll, data received from the aircraft’s transponder resulted in the RIMCAS identifying the aircraft as airborne, even though it was not. As the RIMCAS no longer considered the Embraer 190 to be occupying the runway, it did not detect a conflict when the Boeing 777 began its take-off roll, and did not issue an alert until well after both aircraft had initiated their respective rejected-takeoff procedures and decelerated. The controller was not aware of the conflict before the rejected take-offs, and did not issue instructions to resolve the conflict.  

This occurrence highlights the importance of accurate airborne status being transmitted, received, and validated by these systems to ensure maximum safety benefit. Manufacturers of aircraft transponder systems and of A-SMGCSs with RMCAs, along with certification authorities, and air traffic service providers, are encouraged to work together to ensure that these systems interact effectively to transmit, receive and validate an accurate airborne status. Doing so will ensure that alerts work as intended to reduce the risk of collisions on runways.

The TSB would appreciate being advised of any actions taken in this regard, as they may be included in our investigation report. Upon completion of investigation A20O0029, the Board will release its investigation report into this occurrence.

Yours sincerely,

Original signed by

Natacha Van Themsche
Director of Investigations — Air
Transportation Safety Board of Canada