What happened
On November 7, 1998, a high-risk aircraft proximity occurred near Dublin Airport involving a Lockheed L 1011, registration CS-TEB, and a US Air Force Learjet LJ35, registration 40085.
The incident unfolded during a period of simultaneous operations involving a military training flight at Casement Aerodrome and a commercial approach to Dublin Airport. The Learjet LJ35 was performing VOR/DME approach training for Runway 11 at Casement Aerodrome. During a second missed approach attempt, the military crew was instructed to maintain a specific altitude and eventually turn westerly. However, the aircraft deviated from the required track, flying on a heading of 345 degrees instead of the intended 270 degrees.
At the same time, the Lockheed L 1011 was being radar vectored for an ILS approach to Runway 10 at Dublin Airport. As the military trainer drifted off course, it entered the path of the airliner. The two aircraft came within 1.5 miles of each other, with the Learjet LJ35 positioned approximately 400 feet below the Lockheed L 1011. The crew of the Lockheed L 1011 reported seeing the military aircraft 1,000 feet above them during the encounter.
The investigation
The investigation examined the navigation procedures, air traffic control communications, and meteorological conditions. It was established that the military controller at Casement Aerodrome was operating in a procedural environment without radar facilities. While the Dublin Radar controller identified the incursion and contacted military ATC via landline, the time elapsed between the notification and the military aircraft's corrective turn was only seven seconds.
The investigation also reviewed the various approach charts in use. Discrepancies were noted between the US Navy chart used by the military crew and the official Ordnance Survey and Jeppesen charts. Specifically, the wording regarding when a pilot is "established" on a radial was found to be ambiguous and potentially misleading.
Findings
- The incident was classified as a serious risk of collision.
- The primary cause was poor navigation by the military aircraft and failure to comply with ATC instructions.
- The deviation was exacerbated by the military crew managing a simulated single-engine failure, which increased pilot workload.
- The pilot had declined a full briefing on the approach procedure, believing they were already familiar with it.
- Inconsistably worded approach plates and the lack of radar surveillance at the military aerodrome contributed to the loss of separation.
Safety action
Following the investigation, several recommendations were made to the Standing Civil/Military Air Navigation Co-Ordination Committee (STACMAN), including:
- Re-evaluating the missed approach procedures at Casement Aerodrome to prevent traffic from converging on Dublin Airport's approach paths.
- Standardizing the wording on approach charts, specifically replacing the term "established" with "crossing" to prevent misinterpretation.
- Ensuring all visiting flight crews use charts that are consistent with local aeronautical information.
- Improving notification procedures regarding the level of Air Traffic Services available during military operations.