A U.S. F-15 and a UK police helicopter investigating drone activity came within 1,900 feet of vertical separation during a nighttime encounter. No risk of collision was identified.
A National Police Air Service (NPAS) helicopter dispatched to investigate reports of drone activity near RAF Lakenheath last November had a near miss with what it believed to be an unmanned aerial vehicle, only to later discover it was a U.S. F-15E Strike Eagle.
According to a report published by the BBC and authored by Matt Precey, the UK Airprox Board, which investigates airspace safety incidents, concluded that the helicopter crew had misidentified the red flashing lights of a fast-moving F-15 as belonging to a drone.
The incident occurred on the evening of Nov. 22, 2024, as the NPAS EC135 helicopter responded to a police request to investigate multiple drone sightings near Lakenheath and the surrounding areas.
As the helicopter entered Lakenheath’s airspace, its crew observed what they believed were drones maneuvering nearby. According to the Airprox reportone of the objects “appeared to converge with them and fly above and in front of them,” even overtaking the helicopter at one point. The aircraft came as close as 1,900 feet (579 meters) vertically, prompting the helicopter pilot to classify the risk of collision as ‘medium’.
Here’s an excerpt from the investigation report:
The EC135 Pilot reports that they had flown at 1500ft towards Lakenheath ATZ, contacted Lakenheath Radar on 128.900MHz (the EC135 is not UHF-equipped) and were given a clearance into the zone at 1500ft. They were not informed of any other traffic in the zone and they didn’t receive any traffic returns on their TCAS. They saw red flashing lights in the area of the Lakenheath ATZ (which, at the time, they believed were drones) at a height in excess of 1500ft. [The pilot of the EC135 reported initially that] the ‘drones’ appeared to be carrying out large orbits of Lakenheath airfield. They vacated the zone, and had advised ATC of their intentions to vacate the zone, and then climbed to estimate the height of the ‘drones’.
After climbing to approximately 4000ft, they started heading east towards Bury St Edmunds, tracking a ‘drone’ which was to the north of them at a slightly greater altitude. Several transmissions were made to ATC to explain what they were doing as well as what the ‘drones’ were doing. Once they started heading in a westerly direction (now at 5500ft) one of the ‘drones’ appeared to converge with them and fly above and in front of them.
The investigation determined that this was the Closest Point of Approach (CPA).
By then, they were aware that ATC was speaking to other callsigns (F15s) and the [F15 callsign] was heard but, at the time, they were not aware that they were in the zone. There were still no returns on their TCAS. A descending turn to the left was carried out to increase their perceived separation from the ‘drone’. [The pilot of the EC135 reported initially that] at one stage they had a significant rate of descent at 145kt and the ‘drone’ overtook them, maintaining a constant height above them. Now on a southerly track, they continued the descent to below 2000ft where it appeared that the ‘drone’ was no longer tracking them. There was two-way communication with the pilot of the [F15] during the last direction change, where [the pilot of the EC135] stated that they thought they were being shepherded away from the area and they would return to base. [The pilot of the EC135] cleared with ATC and
returned to base.The pilot and crew of the EC135 commented that they did not observe standard aircraft lights visually and none were picked up on the onboard camera systems. This may have reinforced the crew’s perception that they had observed a drone.
It was only after the Airprox Board reviewed all available information, including flight data and military traffic logs, that it determined the so-called drone was, in fact, a U.S. Air Force F-15 operating under normal conditions out of RAF Lakenheath. The board also noted that Lakenheath Approach Control had not informed the NPAS crew of the fighter’s presence in the area, a lapse that may have contributed to the confusion.
The F-15 pilot reports that, around 2200, [they were] general-handling within an agreed block of SFCFL150 within 20NM of RAF Lakenheath, with Lakenheath Radar Approach Control (RAPCON) ‘Overlord’, on UHF. [The pilot of the F15] remained outside controlled airspace. In line with standard operating procedure, [they were] operating with anti-collision lights, nav lights and formation lights all switched on and they were operating their transponder with Modes A and C. They were paying particular attention to their levels due to the proximity of the controlled airspace to their operating area. Towards the end of the sortie, they received communications on an Operations frequency that a police helicopter was operating in the area. They were initially unable to identify the helicopter using the onboard radar and asked Lakenheath ATC to provide a ‘point-out’ to the helicopter. The Lakenheath controller indicated the helicopter was 12NM range at 5000ft. After receiving the ‘point-out’, they were able to identify [the EC135] track using their onboard radar. They were also able to use other systems to support the crew in maintaining contact with [the EC135]. They then flew towards the helicopter whilst maintaining FL60. At that time, they requested to change to the same frequency as the police helicopter pilot, and they were given a VHF frequency (128.9MHz).
Lakenheath ATC repeatedly issued further Traffic Information to [the pilot of the F15] until the helicopter was sighted visually. [The pilot of the F15] was visual with the helicopter in their 10 o’clock at 1NM, 1000ft below them. Once visual, they utilised onboard sensors to maintain their situational awareness of the helicopter. They heard radio calls between the police pilot and Lakenheath ATC. They maintained at least 1000ft above the helicopter whilst in the vicinity and followed behind. [The pilot of the F15] tried 3 times to call the police pilot on the radio. The police helicopter pilot only responded directly to one of these calls and said something similar to ‘we are going to RTB’. [The pilot of the F15] observed the police helicopter make an aggressive 90-120° turn to the south and descend rapidly. They maintained their level overhead and behind the helicopter. On hearing that the helicopter pilot was returning to base, they turned north to return to Lakenheath.
Therefore, whule the F-15 pilot was aware of the helicopter’s position, the NPAS helicopter crew wasn’t. Investigators suggested it would have been beneficial for Lakenheath ATC to have provided reciprocal traffic information to the EC-135 to enhance situational awareness.
Adding to the confusion, the helicopter’s traffic collision avoidance system did not detect the fighter, likely due to limitations in TCAS functionality at high closure rates and altitudes.
NPAS later clarified that the crew had acted professionally based on the information available to them at the time. “In the absence of any contradictory information, the crew acted on the belief that they were observing drone operations,” said Chief Superintendent Vicki White, according to the BBC. “The crew demonstrated professionalism and sound judgement in identifying a potential hazard.”
The U.S. Air Force confirmed that the F-15 pilot maintained visual contact with the helicopter and complied fully with UK air traffic regulations. A USAF spokesperson added that controllers provided the agreed services to pilots of both aircraft to ensure safety of flight operations.
In the end, the Airprox Board acknowledged that the EC135 pilot had acted in good faith, believing they were observing drone activity. The incident occurred at night, with limited visual references and no night vision equipment on board, making identification more challenging.
However, post-incident analysis revealed that the object was not a drone but a fast-moving F-15 Eagle operating at a greater distance and altitude than initially perceived. Radar data confirmed there had been significant vertical separation, and the Board concluded there was no actual risk of collision. The event was assigned Risk Category E, indicating that safety had not been compromised.
Three contributing factors were identified: the EC135 crew was not made aware of the F-15’s presence by Lakenheath controllers (although not strictly required under Basic Service), had no situational awareness of the fighters, and misidentified the fast jet as a drone due to its lights and trajectory.
It is important to highlight that the close encounter occurred during a period of heightened sensitivity, as multiple alleged drone sightings had been reported over three separate military airfields in the region. These sightings are still under investigation by the Ministry of Defence Police.
Although the was no actual risk of collision, the incident highlights how, at night, lights in the sky can often be misidentified as drones, even by expert eyes, leading to confusion.
Not every light in the sky is a UFO!! The reports about mysterious drones over U.S. bases have created a kind of public hysteria. People are sharing videos of so-called “drones” that, “look like planes”, “sound like planes”, but are clearly just planes! It’s like they’re…
– David Cenciotti (@Cencio4) December 5, 2024
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