What happened
On 27 January 2005, a civilian Embraer 145EU, registration G-EMBE, was cruising at FL210 on Airway P155 near Bedford. The aircraft commander reported seeing a military fighter pass closely in front of his aircraft, approximately 100 feet below and 200 yards ahead, while descending.
The military aircraft involved were two United States Air Force F15E Eagle fighters, flying in formation under the callsign Tahoe 51 and 52. The formation was returning to RAF Lakenheath from a training sortie at Otterburn Range. Due to deteriorating weather and air traffic delays, the formation was low on fuel and had decided to divert to RAF Valley.
During the diversion, the formation commander was managing a high workload, including navigating worsening weather and managing low fuel states. While climbing through FL120, the formation's secondary radar data disappeared. When the aircraft reappeared at a higher altitude, they were no longer flying as a coherent formation. During this period of unmonitored flight, the F15E aircraft entered controlled airspace without transponding, leading to a near-miss with the G-EMBE.
The investigation
An AAIB field investigation established that the military formation was operating with critically low fuel levels. The commander had decided to divert to RAF Valley after observing worsening cloud bases. The investigation examined the radio communications between the formation, Lakenheath ATC, and London Military radar.
It was found that the formation commander inadvertently instructed his wingman to switch to the wrong radio frequency using an auxiliary radio. This error, combined with the high pressure on Lakenheath ATC due to weather, led to a breakdown in communication. Furthermore, the investigation noted that the disappearance of the aircraft's secondary radar data—which effectively disabled the ground radar's conflict alert and the civilian aircraft's TCAS—prevented timely intervention by controllers.
Findings
- The decision to divert due to unforecast poor weather and extended ATC vectoring was made too late.
- The formation commander's high workload, caused by managing low fuel and deteriorating weather, contributed to the error in frequency selection.
- The lack of transponding by the military aircraft while climbing through cleared flight levels prevented the ground radar from providing adequate separation between the formation and the civilian aircraft.
- Inadequate transmission and acknowledgement of clearances within the formation led to the aircraft flying as two separate entities rather than a single formation.
- The loss of secondary radar data for the military aircraft meant that the ground controller had insufficient time to provide adequate separation between the formation and the Embraer 145.