Incident Overview
On 27 July 2009 at 1440 UTC, a Cessna Citation 525 (D-ITAN) and a Boeing 777-300ER (TC-JJA) experienced a serious incident in the London Terminal Control Area. The Citation, operated as an executive flight, departed from London City Airport on a DVR 4T Standard Instrument Departure (SID). The Boeing 777, operated by Turkish Airlines as a commercial passenger flight, was being vectored for an ILS approach to Runway 27R at London Heathrow Airport.
Sequence of Events
The Citation crew received an ATC clearance to climb to and maintain 3,000 ft but read back an altitude of 4,000 ft. The Tower controller did not notice the error. After takeoff at 1436 hrs, the Citation climbed at a high rate, reaching 3,000 ft and continuing to climb. At 1437:28 hrs, the crew was instructed to contact Thames radar. Meanwhile, the Boeing 777 was cleared to descend to 4,000 ft. At 1437:38, the 777 crew acknowledged a turn onto a heading of 185°.
At 1438:05, the 777 crew transmitted a traffic alert. Three TCAS Resolution Advisories (RAs) were generated in quick succession on the 777: a 'crossing descend' RA, an 'increase descent' RA, and a 'reversal climb' RA. The 777 crew did not follow the RAs; the commander later stated that he judged a descent would increase collision risk and took control to follow the climb RA. The Citation was equipped with TCAS I, which does not generate RAs, and its crew reported no traffic advisories.
At 1438:19, the two aircraft passed on nearly reciprocal headings with a lateral separation of approximately 0.5 nm and a vertical separation of 164 ft, the Citation being below the 777. The Citation crew saw the 777 and took avoiding action by turning left. The radar controller later instructed the Citation to descend to 3,000 ft, then climb to 4,000 ft after the conflict.
Key Findings
The investigation noted that the Citation crew misinterpreted the altitude clearance, reading back 4,000 ft instead of 3,000 ft, which the Tower controller did not catch. The 777 crew did not comply with TCAS RAs, and the aircraft's flight recorders were overwritten before data could be retrieved. The Citation had no crash-protected recorders. Five safety recommendations were made, though their details are not specified in this summary.