C525 / B773, vicinity London City UK, 2009
C525 / B773, vicinity London City UK, 2009
On 27 July 2009, a Cessna 525 departing from London City failed to comply with the initial 3000 feet QNH SID Stop altitude and at 4000 feet QNH in day VMC came into close proximity on an almost reciprocal heading with a Boeing 777-300ER. The 777, on which line training was being conducted, failed to follow any of the three TCAS RAs generated. Actual minimum separation was approximately 0.5nm laterally and estimated at between 100 feet and 200 feet vertically. It was noted that the Cessna had been given a stepped climb SID.
On 27 July 2009, a Cessna 525 being operated by Stuttgart-based company Eisele Flugdienst and departing from London City on a passenger charter flight failed to comply with the initial 3000 ft Altimeter Pressure Settings SID stop altitude and at 4000 ft QNH in day Visual Meteorological Conditions (VMC) came into close proximity on an almost reciprocal heading with a Boeing 777-300ER being operated by Turkish Airlines on a scheduled passenger flight from Istanbul Atatürk to London Heathrow as a Line Training sector. Actual minimum separation was approximately 0.5 nm laterally and estimated at between 100 ft and 200 ft vertically. There were no injuries to any of the 248 occupants of the Boeing 777 or to the 3 occupants of the Cessna.
An Investigation into this event was carried out by the UK AAIB after it was assessed as a Serious Incident. The Investigation found that the Boeing had been in compliance with its clearance to descend to 4000 ft prior to the event. It was also found that:
- The context for the event was an unexceptional ATC workload.
- The failure of the Cessna flight crew to correctly fly the SID had followed the undetected incorrect readback of the Departure Clearance given.
- Airborne Collision Avoidance System (ACAS) equipment on both aircraft functioned normally during the event.
- The Cessna was equipped with TCAS 1, which only provides TAs. After the event, the pilot stated that no TA had been annunciated, despite the fact that correctly functioning equipment would have been expected to do this.
- Flight Crew Line Training was being conducted on the Boeing 777 with the First Officer as PF and a third pilot of unspecified status occupying the right hand observer seat.
- The Boeing 777 received three successive TCAS RAs - crossing descend, increase descent and reverse climb but failed to follow any of them, contrary to the universal SOPs contained in ICAO PANS-OPS.
- The Cessna crew acquired the Boeing visually in sufficient time to take effective avoiding action and did not believe that there had been any (actual) risk of collision.
- Only an observer pilot in the right hand supernumerary seat in the Boeing flight deck saw the Cessna during the encounter
- Short Term Conflict Alert (STCA) activation occurred, which was reportedly not unusual with high initial climb rates of aircraft departing from London City, but did not provide sufficient time for ATC to react to the level bust in time to prevent the consequences.
It was also noted that:
- Departure clearance had not been requested by the Cessna when the crew called for start and so the approval to start was accompanied by this clearance. The readback was both incomplete and given with the wrong stop altitude and the ATCO had corrected the omission but missed the stop altitude error.
- R/T communications by the Boeing in respect of their TCAS activation were not in compliance with the universal SOP for such calls contained in ICAO PANS-ATM.
- Departures from London City “require crews to make full power take offs before leveling off less than one minute after leaving the ground which is unusual”.
- There had been a delay in notifying the event to the AAIB.
- No recorded flight data was available from the Boeing because by the time it was requested, the Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) had been overwritten and the data from the QAR, which had sufficient data storage capability to have included the event, was not available due to “system failure”. The Cessna was not fitted with any voice or data recorders and was not required to be.
- The Boeing TCAS had incorrectly identified the Cessna as being not Mode ‘S’ equipped but the ANSP radar had received Mode ‘S’ data from it.
- There was a history of SID-busting in the London area where low initial stop altitudes existed and the consequences of this were potentially high risk because of regularly used tracks only 1000 ft above.
- “Had the revised ICAO (SID R/T phraseology) procedures been adopted by the UK, it is likely that this incident would have been prevented because (the Cessna) would have levelled off at 3000 ft regardless of its cleared altitude.”
It was concluded by the Investigation that the arguments for and against implementation of the revised ICAO (SID R/T phraseology) procedures by the UK were “… beyond the scope of this report and, since ICAO is already working to resolve the situation, no recommendations are made on this topic beyond endorsing the need for urgency in reaching a resolution.”
A total of five Safety Recommendations were made as a result of the Investigation:
- It is recommended that NATS demonstrates to the Civil Aviation Authority (CAA) that appropriate mitigation has been put in place to reduce significantly the risk of an accident resulting from a level bust by an aircraft departing London City Airport or on the base leg turn positioning to land at Heathrow Airport. (2010-056)
- It is recommended that London City Airport amends all Standard Instrument Departures (SIDs) so that they terminate at an altitude of 3000 ft. (2010-057)
- It is recommended that London City Airport removes Step Climb procedures from its Standard Instrument Departures (SIDs). (2010-058)
- It is recommended that the Directorate General of Civil Aviation of Turkey ensures Turkish Airlines TCAS training complies with the Airborne Collision Avoidance System Training Guidelines contained in ‘ICAO PANS-OPS (Doc 8168)’. (2010-059)
- It is recommended that the Civil Aviation Authority considers whether the carriage of TCAS II should be mandated for aircraft operating in those parts of the London TMA where London City Airport SIDs interact with traffic positioning to land at Heathrow Airport. (2010-060)
The Final AAIB Report was published on 9 September 2010 and may be seen in full at SKYbrary bookshelf: AAIB Bulletin: 9/2010 EW/C2009/07/07
NATS made the following comment regarding this incident:
"Within a few days of this event, NATS instigated a number of measures to reduce the likelihood of recurrence of the direct cause of this loss of separation (no detection of incorrect readback). These focussed on methods to increase pilots’ awareness of the level restriction on the SID (a briefing pack), as well as techniques to assist controllers detect an incorrect readback (use of active listening techniques).
The NATS’ investigation into the event included analysis of historical data about previous events involving London City departures interacting with Heathrow inbounds. Evidence indicated that an unsafe interaction in this portion of airspace was just as likely to result from an aircraft inbound to Heathrow descending below its cleared altitude as from an outbound aircraft busting its level. Consequently further actions by NATS focussed on addressing both situations.
It was identified that one of the factors leading to a London City departure busting its level was the requirement for the aircraft to level off below the final SID altitude, effectively introducing a stepped climb to the SID. A proposal was therefore made to the CAA’s Directorate of Airspace policy that the SID should terminate at 3000’. This change to the SID has subsequently been agreed and took effect on 23rd September 2010.
One of the most common causes of level bust by a Heathrow inbound aircraft in this portion of airspace is selection of an incorrect pressure setting by the pilot. To mitigate the effect of this, NATS has developed a “Barometric Pressure Setting Advisory Tool” (BAT), which uses down- linked Mode S data to alert controllers to an incorrect QNH setting. This tool will be available to London Terminal Control ATCOs from November 2010.
In the meantime and in order to manage the risk whilst awaiting implementation of these mitigations, NATS instigated a temporary procedure whereby 2000’ vertical separation (as opposed to the standard 1000’) was provided in a defined portion of airspace where the London City SID track interacted with the Heathrow inbound track in order to build in a greater safety margin should an aircraft bust its level. This required that controllers did not clear Heathrow inbound traffic below 5000’ until clear of the London City departure track. Prior to implementation of these changes, airline operators were involved in a number of discussions, specifically around any potential effect on the landing rate at Heathrow and the possibility of unstable approaches. As a result of these discussions, both these areas have been monitored closely throughout the period the procedure has been in use to ensure that a safe and expeditious level of service was provided at all times.
Following the change to the SID in September, the 2000’ procedure will only be invoked during periods of low pressure (as it will then only be required to mitigate the situation when an inbound aircraft busts its level), and it is planned to remove it completely following introduction of the BAT."
- Loss of Separation
- Airspace and Procedure Design
- Standard Phraseology
- Pilot-Controller Communications (OGHFA BN)
- Speed and Timeliness of Communication
- Level Bust - Pilot Induced Situations
- ACAS Response and Level Bust Hazard
- Incorrect use of TCAS Traffic Display
- TCAS Occurrence (OGHFA SE)
U.K. Civil Aviation Authority (CAA). Civil Aviation Publications