Event Details

Title:Altitude bust and AIRPROX, Boeing 737-236, G-BKYC, and Illyushin IL 76, No 78807, 16 July 1997
Micro summary:An altitude bust by an IL-76 and two Su-30s puts a Boeing 737 at risk.
Event Time:1997-07-16 at 1425 UTC
File Name:1997-07-16-UK.pdf
Publishing Agency:Aircraft Accident Investigation Board (AAIB)
Publishing Country:United Kingdom
Report number:EW/C97/7/3
Site of event:3.5 nm north of Reading (10 nm east of Compton VOR)
First AirplaneSecond Airplane
Departure:UnknownKhrabrovo Airport, Kalininggrad, Russia
Destination:UnknownRAF Fairford, Fairford, England
Airplane Type(s):Boeing 737-236Illyushin IL 76
Flight Phase:CruiseDescent
Operator(s):British AirwaysUnknown
Type of flight:RevenueMilitary
Serious Injuries:00
Other Injuries:00
Executive Summary:The Military IL76 tanker aircraft (callsign WS78807), in formation with two SU30 fighters inbound to RAF Fairford for the Royal International Air Tattoo 1997, was routed through controlled airspace as General Air Traffic (GAT), referred to in this report as 'civil traffic'. It had flight planned as Operational Air Traffic (OAT) in accordance with procedures agreed for military traffic inbound to RAF Fairford. The formation was cleared by ATC to descend to FL160 as it transited the London Terminal Manoeuvring Area (LTMA) inbound to the Compton VOR (CPT) from the east. Instead of indicating level at FL160 the ATC controller noticed that the IL76's height readout (Mode 'C') was indicating 200 feet below its assigned level at FL158. The Boeing 737, en-route from Glasgow to London Gatwick was level at FL150, at an Indicated Air Speed (IAS) of 300 kt and approximately 7 nm north-east of the formation as the IL76's height readout reduced further to indicate FL156 (600 feet above that of the Boeing 737). The Boeing 737 was given 'avoiding action' by ATC and instructed to turn left onto a heading of 090. The Boeing 737 passed 0.5 nm north of the formation in a steeper than normal left turn. Its position at the time was 3.5 nm north of Reading (10 nm east of the Compton (CPT) VOR). The weather at the time was good with light turbulence and unlimited visibility above 8/8ths cloud cover.

AAIB Conclusions

The commander of the Russian formation had received and understood the procedures and routings for traffic inbound to the UK for the Royal International Air Tattoo at Fairford. He and his crew understood little English but were capable of operating safely within the UK UIR/FIR so long as their planned flight was conducted in accordance with their expectations. The pilots of the two SU30 aircraft, who spoke little English, were fully reliant on the actions of their formation leader in order for them to arrive safely at their destination. They were not in two way communication with the civil ATC agencies.

The unexpected re-routing of the formation as it approached the eastern coast of the UK was unexpected and unsettling to the crew. The CLACTON SC was aware of the difficulties in communicating with the formation and that the mention of unexpected and unfamiliar reporting points led to confusion. He was not aware that the formation intended to route as military traffic outside controlled airspace under the control of military agencies. The formation however eventually complied with ATC instructions as it was routed towards the London Terminal Manoeuvring Area. The LMS CSC had noticed the apparent poor level keeping of the formation and had considered suggesting to the LMS SC that it might be prudent only to descend the IL76 formation to FL170 until it was clear of the track which Gatwick inbound aircraft would follow at FL150. However before his suggestion was adopted the formation was cleared to FL160.

The pilots of the two SU30s were able to maintain a close formation with their 'tanker' (the IL76). Had either one experienced an in-flight emergency necessitating a break in formation and an emergency diversion the subsequent control of that aircraft would have been difficult to say the least. The pilot would have taken a finite time to change frequency to that of the current controlling sector and would not have been able to understand the subsequent ATC instructions.

No doubt the CLACTON SCs would have been aware that the military ATC agencies would have been better suited to provide a service to this military formation. However, given the communication difficulties which the sector controller was experiencing with the IL76 formation, it is possible that they concluded that attempting to divert the pilot from what they thought was his intended route would have created more problems than it would have resolved. Even if the TOI had been available to the relevant sector controllersit did not include any specific mention of the problems that can be associated with formations, especially within congested controlled airspace. The controllers, however, were instantly aware that the formation was apparently not adhering to its assigned level and instigated the appropriate avoiding actions.
Learning Keywords:Operations - Airspace - Air Proximity
Operations - Airspace - Air Traffic Control
Operations - Language


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