Incident Report Airprox AFR 1482
An Air France Airbus A319 lost separation with a Czech Airlines Boeing 737-500 near the ILS for Runway 24 at Prague
An Airbus A319 followed the track shown on the FMS (the radio failure procedure) rather than continuing on the heading anticipated by the air traffic controller and written in the STAR text. This led to a loss of separation with a Boeing 737 on the final approach course. The minimum separation was 1.7nm.
The main threats & errors during this incident can be summarised as follows:
- Failing to adhere to the air traffic control strategic plan in the TMA can lead to a loss of planned safe separation with potential for mid-air collision; loss of control in attempting to avoid a mid-air collision; and wake vortex induced loss of control accident types.
- Misunderstanding of standard ATC procedures in TMA on the STAR by the Pilot Flying.
- Failure of PF (captain) to respond to the PM (co-pilot) prompt for clarification of the air traffic controller’s expected route.
- Failure by flight crew to recognise the right turn towards traffic tracking from left to right on the TCAS display would lead to a slow merging conflict
- Failure to respond to the ATCO turn instruction in a short time period to deconflict the two aircraft.
- Failure of the ATCO to use the phrase “avoiding action” to alert the crew to the urgency of the response required.
The main learning points from this incident were:
There can be a significant difference between the STAR (which is usually published as a defined route for radio failure and surveillance failure contingency procedures) and the expected normal radar vectoring/sequencing track to be followed. Letting the autopilot/FMS follow the STAR to the instrument approach procedure rather than following the ATC instructions or STAR expected written instructions can lead to a loss of separation. However, terrain clearance should be assured if the STAR/IAP has been designed correctly.
There can be a perceived difference in hazard between air traffic controllers and pilots. The ATCO will try to avoid short term conflict alert triggering but pilots may be unconcerned unless ACAS triggers at least a Traffic Advisory. There was a merging conflict detected by the ATC system that the ACAS system on-board the aircraft would take longer to detect and resolve.
The wording of “unless otherwise instructed” leaves the case of the expected track in the event of air-ground-air communication failure open to interpretation. Do flight crews always brief what will happen for this event?
The investigators did not state why they thought the aircraft turned when it did. Clarification that it had picked up the IAP for the ILS runway 24 would have been useful.
The ATCO did not use the phrase “Avoiding Action” which may have alerted the flight crew to the urgency of the response required.
What may have appeared as a (Andrew insert a TCAS diamond here as you would see on the screen) on the TCAS display 3.4 nautical miles ahead crossing left to right at 07:53:51 would have become a slow merging collision threat if the A319 continued to track to intercept the localizer from the right.