What happened
On August 18, 2006, a Boeing 737-73S, registration D-AHIF, operating flight HHI5753 from Izmir Adnan Menderes (LTBJ) to Bremen (EDDW), experienced a loss of two-way radio communication while transiting European airspace. The loss of contact was first noted while the aircraft was operating in the Bratislava FIR. Following established procedures for a communications failure, the crew set their transponder to SSR code 760 and continued along their filed flight plan.
As the aircraft entered the Prague FIR at flight level 380, it remained without communication with Prague Control. Due to the inability to establish contact, the Czech Air Force scrambled JAS 39 Gripen fighter aircraft (QRA) to intercept the airliner. The interception was conducted according to standard procedures. During the encounter, the QRA pilots established contact with the crew of D-AHIF on the emergency frequency 121.5 MHz.
Through this emergency link, the crew informed the intercepting pilots of their technical difficulties, specifically that they could receive transmissions but were unable to transmit messages. The QRA pilots then instructed the crew to switch to the appropriate Prague Control sector frequency. Once the crew tuned to the new frequency, they were able to receive instructions from ACC Prague via one-way communication and confirmed their presence by performing a Squawk Ident.
The investigation
The ÚZPLN investigation focused on the sequence of events and the technical state of the aircraft's communication systems. The investigation established that the crew followed all appropriate procedures for handling a loss of communication. The investigation also reviewed the actions taken by Air Traffic Control (ATC) and the military interception unit, finding that all parties acted in accordance with established protocols.
Following the incident, a ground inspection of the aircraft was conducted. This inspection revealed significant hardware issues affecting the aircraft's VHF capabilities. Specifically, corrosion was discovered on the antenna for VHF radio #1, and a disconnected connector was found on the antenna for VHF radio #2. Both radio units were subsequently replaced.
Findings
- The primary cause of the loss of two-way communication was a technical failure of the aircraft's VHF radio systems.
- Corrosion on the VHF #1 antenna and a disconnected connector on the VHF #2 antenna prevented the crew from transmitting messages to ATC.
- The crew of D-AHIF acted correctly by utilizing the 7600 SSR code and following standard loss-of-communication procedures.
- The interception by the Czech Air Force QRA was performed according to standard operating procedures.
Safety action
- The aircraft operator should implement procedures to ensure greater attention to the airworthiness and functional integrity of aircraft radio communication systems.