What happened
On 16 June 2015, a BAe 125-800B, registration N1310H, departed Kerry Airport for a transatlantic flight to Canada. During the departure phase, the aircraft was cleared to a stop climb at Flight Level 200. However, shortly after transferring to Shannon Low Level Control, the flight crew reported that they were level at Flight Level 200, but radar data indicated they had actually leveled off at only 2,000 feet.
This altitude discrepancy placed the aircraft in close proximity to the Slieve Mish mountains, which reach elevations of approximately 2,800 feet. Upon noticing the discrepancy, Shannon controllers immediately intervened, instructing the crew to climb to Flight Level 300 and to expedite their ascent through 4,000 feet to clear the high ground. The crew complied, and the flight continued without further incident.
The investigation
The AAIU examined communications between the Kerry Tower and Shannon Low Level controllers, as well as the pilot's account of the event. The investigation looked into the specific instructions provided during the taxi and takeoff phases. It was noted that the Kerry Tower controller used the phrase "Flight Level Two Hundred" when relaying the stop climb instruction.
Investigators also reviewed the operational status of air traffic monitors at Kerry and Knock airports. It was discovered that despite previous commitments to have these monitors operational by mid-2014, the systems were not yet fully functional at the time of the investigation, which limited the radar information available to the Kerry controller.
Findings
- The aircraft leveled off at 2,000 feet, which was significantly lower than the cleared altitude and placed it at risk of terrain impact.
- The primary cause was the flight crew's misinterpretation of the altitude clearance; the crew stated they were unsure of the meaning of "Flight Level Two Hundred" and leveled at 2,000 feet to avoid exceeding any perceived limits.
- The crew did not seek clarification from air traffic control when they were uncertain about the assigned altitude.
- While the Kerry controller used non-standard phraseology ("Flight Level Two Hundred"), the investigation determined this was not the origin of the crew's confusion.
- The lack of operational air traffic monitors at the airport hindered the ability to provide certain radar oversight.