Event Details

Title:Loss of separation, Boeing 747 and Gulfstream G IV accident report
Micro summary:Loss of separation between a Boeing 747 and a Gulfstream IV.
Event Time:1997-07-03 at 1443 UTC
File Name:1997-07-03-UK.pdf
Publishing Agency:Aircraft Accident Investigation Board (AAIB)
Publishing Country:United Kingdom
Report number:EW/C97/7/1
Site of event:14 nm east of Lambourne VOR
Latitude/Longitude:5138.73N 00034.2E
First AirplaneSecond Airplane
Departure:Kansai International Airport, Osaka, JapanCosta Smeralda, Olbia, Sardinia
Destination:London Heathrow Airport, London, EnglandLondon Luton Airport, London, England
Airplane Type(s):Boeing 747-300Gulfstream IV
Flight Phase:ApproachApproach
Operator(s):Japan AirlinesITT Corporation
Type of flight:RevenueCorporate
Serious Injuries:UnknownUnknown
Other Injuries:UnknownUnknown
Executive Summary:A loss of separation occurred between a Boeing 747-300 (B 747) and a Gulfstream IV (G IV) in the London Terminal Control Area, which is Class A controlled airspace. The B 747 was en route from Kansai, Japan, to London (Heathrow) Airport; the G IV was en route from Olbia, in Sardinia, to London (Luton) Airport.

The B 747 began its descent after entering the UK Upper Information Region (UIR) from Holland and was controlled through the Clacton Sector for arrival at London Heathrow. It was cleared initially to Flight Level (FL) 290 then FL 150, and later to FL 110, whilst routing direct to the Lambourne VOR and maintaining 290 kt. On making contact with Heathrow Intermediate North Director the B 747 was cleared to descend to FL 90, to leave Lambourne on a heading of 270, and to reduce speed 'now' to 210 kt.

The G IV entered the UK FIR from France and was controlled through the Lydd Sector for arrival at Luton via the Detling VOR. When the G IV contacted the Lambourne controller it was level at FL 130 and was permitted to maintain high speed whilst given a radar heading of 340, it was subsequently cleared to FL 120.

As the G IV reached FL 120 the pilot reported that his Traffic Alerting and Collision Avoidance System (TCAS) was indicating traffic in his one o'clock position. The controller initially thought that there was 1,000 feet vertical separation between the two aircraft and declared this, but he then gave the G IV avoiding action, after the pilot reported that the traffic was 300 feet below him, to turn to the left which took it out of the path of the B 747.

At the same time the B 747 crew complied with the first of two TCAS Resolution Advisory (RA) messages. The first instruction was to climb followed by a subsequent instruction to descend. Subsequent analysis of the recorded radar data showed the closest proximity of the two aircraft was 0.83 nautical miles (nm) horizontally with vertical separation of 100 feet; the next element of the recorded radar data indicates that the vertical separation had then increased to 200 feet with the horizontal separation reducing to 0.66 nm.

The following causal factors were identified:

1. The B 747, having left FL 120 then stopped descending some 300 feet below this level whilst reducing speed from 290 kt to 210 kt. FL 120 was assigned to the G IV by the bandboxed Terminal Control North East Departures/Lambourne controller before the proper vertical separation had been established after its direct routing towards Luton had brought it into lateral conflict with the B 747.

2. The North East Departures / Lambourne controller did not apply the procedure given in MATS Part 1 regarding level assessment of SSR Mode C (height information) when giving clearance to the G IV to FL 120. The controller should have waited for the B 747 to have had a readout of at least FL 116 (400 feet below the vacated level) before clearing the G IV to descent. The controller then did not monitor the Mode C readout of the B 747 to ensure that it was 'continuing in the anticipated direction'.

3. Despite reporting to the Heathrow Intermediate North controller that the aircraft had vacated FL 120, the B 747 did not descend at the minimum rate mandated for the UK and detailed in the UK Air Pilot (500 ft/min). If it was not possible to comply with this requirement, the crew were required to inform the controller but did not do so.

4. The Heathrow Intermediate North controller unaware that the aircraftspeed was 290kt called for a combined speed and level change which resulted in the B 747 having a minimal rate of descent while its speed reduced.

5. The B 747 crew did not report their speed control, which had been imposed by Clacton SC, to the Lambourne Sector, thereby allowing the controllers to assume a standard speed of 250 kt.

6. Since the TCAS manoeuvre was not fully co-ordinated by both aircraft's TCAS, one of which was not selected to TA/RA, the B 747's initial RA reduced the separation distance.
Learning Keywords:Operations - Airspace - Air Proximity
Operations - Airspace - Air Traffic Control
Operations - Airspace - TCAS
Operations - Language


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