History of the Flight
The aircraft, a Boeing 737-8F2 registered TC-JKF, was operating a scheduled passenger flight from London Stansted Airport to Ankara, Turkey. After an uneventful start-up and taxi, the tower controller issued a clearance to line up on Runway 22 and depart on the Clacton 8R Standard Instrument Departure (CLN 8R SID). The controller observed the takeoff and initial climb, which appeared normal. He looked away briefly; when he looked back, the aircraft was in a steep nose-down attitude and descending before it levelled off. The local controller tried twice to establish communications but received no reply, then contacted the departure controller at Swanwick, who confirmed the aircraft was on his frequency. The tower controller observed the aircraft flying a low‑level left turn before commencing a climb.
The co-pilot, who was pilot flying, had selected 800 ft on the Mode Control Panel (MCP) before takeoff. Shortly after takeoff he engaged the autopilot; the aircraft pitched nose down and, after reaching a maximum altitude of approximately 1,050 ft, descended to 800 ft aal. The pilots contacted London Control and passed their callsign along with the SID designator. This frequency change took place before Stansted tower instructed them to do so, which is contrary to the SID instructions. The departure controller requested the passing and cleared altitude; when the pilots asked to repeat, the request was repeated. After the second request, the pilot transmitted that he was "Now eight thousand eight hundred feet". The altitude readout on the radar screen showed 800 ft, and the controller asked the pilot to confirm 800 ft and reiterated his request for the cleared altitude. The pilot replied "Altitude eight hundred, six sixty now". The aircraft had entered a left hand turn and continued flying the lateral part of the CLN 8R SID, which consisted of a turn through approximately 130° to roll out on a track of 088° towards the Clacton VOR. During this turn, the first part flown level at approximately 450 ft agl, the pilot reported that the autopilot disengaged and that he received "Pull up" and "Don't sink" GPWS warnings. The controller asked for confirmation of climbing to 4,000 ft; the pilot replied he was 'Now climbing four thousand'. The aircraft selected altitude on the ATC radar screen changed from 800 ft to 3,200 ft, and after the pilot confirmed climbing to 4,000 ft, the readout changed to 3,200 ft. The aircraft entered a climb having turned through approximately 100°. The remainder of the departure proceeded without further incident.
The commander of the aircraft was on his third flight to a UK airport and his second flight to Stansted. On the previous departure from Stansted he flew a Dover SID without incident. The first officer was on his first flight into Stansted.
Interpretation of Chart Information
The pilots were using Jeppesen charts. The CLN 8R SID chart contains a general information panel at the top. Items 3, 4 and 5 state: '3. Initial climb straight ahead to 850'; '4. Cruising levels will be issued after take-off by LONDON Control'; '5. Do not climb above SID levels until instructed by ATC'. The information displayed on the Jeppesen chart reflects the UK AIP, though the UK AIP states 847 ft instead of 850 ft.
The captain stated that he set 800 ft on the MCP because he interpreted the instructions to mean he was required to level the aircraft at 850 ft and not climb above until instructed by London Control. It was not possible to select exactly 850 ft on the MCP as altitudes are selectable only in increments of 100 ft, so he selected 800 ft, the nearest value not exceeding the perceived 850 ft clearance limit.
The analysis in the report noted that the phrase "Initial climb straight ahead to 850 ft" is grammatically similar to ATC phraseology "Climb to altitude 850 ft". The pilots interpreted 850 ft as the first SID level they were required to maintain pending further ATC instructions. The instruction "Do not climb above SID levels until instructed by ATC" was taken to mean they must obtain positive ATC clearance to climb above any levels specified on the SID.
The commander’s previous experience on a Dover SID, which uses the phrase "No turns below 850 ft", reinforced the misinterpretation. The investigation revealed that vertical profile information in the general information section of SIDs was misinterpreted.
Safety Recommendation
As a result of this incident, NATS harmonised the general information section of published SIDs so that, where the phrase 'Initial climb straight ahead to...' occurs, it is replaced by 'No turns below…'. This action was applied only to airports within the London TMA.
Safety Recommendation 2011-089 was made: It is recommended that the Civil Aviation Authority should ensure that the vertical profile information included within the general information section of all SIDs published in the UK AIP is unambiguous and that the wording used is consistent across all UK SIDs.