What happened
On April 18, 2006, a Viet Nam Airlines Boeing 777-2Q8ER, registration VN-A149, flying flight HVN 545 from Hanoi to Frankfurt, entered the Prague Flight Information Region (FIR) without establishing radio contact with air traffic control. The aircraft had previously been flying through the Warsaw FIR without two-way communication, a situation noted by radar controllers in both Warsaw and Prague.
As the aircraft continued its flight path at FL 360, Prague ACC attempted to establish contact via the international emergency frequency (121.5 MHz) multiple times without success. Due to the lack of communication, the Czech Air Force initiated a Quick Reaction Alert (QRA) interception using JAS 39 Gripen fighter jets.
At 03:56 UTC, while flying near Prague, the crew of the Boeing 777-2Q8ER noticed the intercepting fighters and responded on the emergency frequency. During the encounter, a military controller provided the crew with an incorrect sector frequency, which was subsequently corrected by Prague ACC. Two-way communication was successfully established on the proper sector frequency at 03:58 UTC, and the crew was informed of the reason for the interception. The intercepting aircraft then performed a separation maneuver to clear the airway.
The investigation
The ÚZPLN investigation examined the radio communication logs, the sequence of events in both civilian and military control centers, and the crew's actions. The investigation looked into why the crew failed to respond to repeated emergency calls and analyzed the coordination between Prague ACC and the military control center (MACC EC) during the interception and subsequent release of the QRA aircraft.
Findings
- The crew of the Boeint 777-2Q8ER failed to establish two-way radio communication with the appropriate ATC units in the Warsaw and Prague FIRs as required by standard procedures.
- The crew did not respond to multiple attempts by ATC to reach them on the 121.5 MHz emergency frequency, despite the messages containing clear identification of the aircraft.
- The primary cause was the failure to establish two-way communication on the appropriate frequencies according to established procedures for the FIRs being traversed.
- During the interception, a technical error occurred where a military controller provided an incorrect frequency to the crew due to a discrepancy in channel spacing (25 kHz) on remote monitoring equipment.
- Coordination deficiencies were noted between civilian and military centers, including a temporary loss of communication between ACC Praha and MACC EC, and a deviation from the coordinated procedure during the QRA aircraft's release maneuver.
Safety action
- The aircraft operator should implement procedures to ensure crews pay greater attention to border crossings between FIRs and fulfill their obligation to establish two-way radio contact with the relevant ATC units.