Inaccurate Airborne Status Transmitted by Transponders and its Effect on Runway Monitoring and Conflict Alert Systems - Civil Aviation Safety Alert (CASA) No. 2021-03

Attention:

All air operators, air navigation services providers

File Classification No.: Z 5000-35 U
RDIMS No.: 17157642
Document No.: CASA 2021-03
Issue No.: 01
Effective Date: 2021-05-03

Purpose:

The purpose of this Civil Aviation Safety Alert (CASA) is to raise awareness to aircraft owners, operators and Air Navigation Services Providers (ANSP) on an issue related to operation of aircraft equipped with the Honeywell Primus Epic integrated avionics system transponders.

Background:

The Transportation Safety Board (TSB) recently advised Transport Canada of an occurrence at Toronto/Lester B. Pearson International Airport (CYYZ) where immediately following a rejected takeoff, an Embraer 190 (E190) equipped with a Honeywell Primus Epic integrated avionics system transponder incorrectly transmitted that the aircraft was in airborne status but remained on the runway.

A second aircraft, a Boeing 777-300 (B777) readying for take-off had been issued a take-off clearance while the E190 remained on the runway. Although the E190 flight crew made a radio call to the tower that they were aborting the takeoff, at the same time the B777 read back its take-off clearance on the same control tower frequency and commenced its take-off roll. The simultaneous radio transmissions went undetected and neither air traffic control nor the B777 flight crew heard the abort radio call of the E190.

Immediately after beginning its take-off roll the B777 flight crew observed that the E190 was still on the runway and initiated a rejected takeoff. The B777 came to within 3800 feet from the E190.

In the initial assessment in its investigation (TSB investigation A20O0029)the TSB has found that the Honeywell Primus Epic integrated avionics system in the E190 uses software logic that determines the aircraft to be airborne when the aircraft’s indicated airspeed exceeds 50 knots. The result being that the aircraft transponder may transmit that the aircraft is airborne when the aircraft may still be on the ground.

Additionally, the runway incursion monitoring and conflict alert system (RIMCAS) used by the air navigation service provider (ANSP) at CYYZ was configured to use data from the aircraft’s transponder transmission as the primary indication that an aircraft had become airborne. Therefore when the E190 exceeded 50 knots on its departure roll, the RIMCAS identified the aircraft as airborne even though it was not. As a result of this system logic, the RIMCAS did not detect a conflict when the B777 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.

In December 2020, NAV CANADA published an Urgent ATC Information Bulletin for all Toronto Tower personnel. The bulletin cautioned controllers that RIMCAS Stage 1 and Stage 2 alerts may not be generated when Embraer E-jets and some aircraft manufactured by Dassault, Gulfstream, Learjet, and Textron Aviation (formerly Cessna) are departing. The bulletin also advised that Stage 1 and Stage 2 alerts may not be produced for aircraft or vehicles approaching the active runway when one of these aircraft types is departing, and controllers were reminded to monitor these situations closely. NAV CANADA is investigating options for RIMCAS software mitigations.

Transport Canada is in the process of communicating with the original equipment manufacturer (OEM) to address the current software logic to identify aircraft airborne status. Additionally, Transport Canada is in the process of communicating with applicable ANSP who have similar RIMCAS that could yield a comparable outcome with aircraft with similarly configured transponders.

Recommended action

  1. Air operators currently operating aircraft equipped with Honeywell Primus Epic integrated avionics system should provide the information found in this CASA to staff and/or flight crew as a means of awareness.

Contact office:

For more information concerning this issue, contact a Transport Canada Centre; or contact Commercial Flight Standards in Ottawa by e-mail at AARTFInfo-InfoAARTF@tc.gc.ca.

Original signed by

Félix Meunier
Director
Standards

The Transport Canada Civil Aviation Safety Alert (CASA) is used to convey important safety information and contains recommended action items. The CASA strives to assist the aviation industry's efforts to provide a service with the highest possible degree of safety. The information contained herein is often critical and must be conveyed to the appropriate office in a timely manner. The CASA may be changed or amended should new information become available.