Misinterpretation of altitude restrictions led an­ AnadoluJet Boeing 737-800 to level off at just 450ft (137m) after leaving London Stansted - an incident extraordinarily similar to that involving another Turkish 737 five years before.

Bound for Ankara on 13 March last year, the aircraft - TC-JKF - had been cleared to follow the Clacton 8R standard instrument departure from runway 22. However, the Clacton 8R chart includes a note requiring the initial climb to be straight ahead, until reaching 850ft.

While the note intended to convey a no-turning instruction, the pilots misinterpreted this to mean that the aircraft needed to level off at 850ft and await air traffic control instructions to climb further. This view was reinforced by the chart, which specifically told crews not to climb above standard instrument departure levels until cleared.

The co-pilot, flying, had pre-selected an 800ft altitude on the control panel. When the crew engaged the autopilot after take-off, the aircraft - which had reached 1,050ft - pitched nose-down to capture the requested height - a manoeuvre noticed by the Stansted tower controller.

The aircraft executed a left turn about 450ft above the ground, during which the autopilot disengaged and the ground-proximity warning system sounded, before controllers ordered the jet to climb to 4,000ft.

Neither pilot had operated into the UK more than a couple of times, and only the captain had previously flown into Stansted. Ironically, the captain's prior departure from Stansted had been along the Dover pattern - the scene of a similar chart confusion involving a Turkish Airlines 737-800 in 2006, when the jet levelled at 500ft.

That incident highlighted potential confusion over the 'straight ahead' instruction on the departure chart. In the wake of the Anadolu incident, the Air Accidents Investigation Branch has recommended that vertical profile information on UK charts is made "unambiguous" and "consistent".

Source: Flight International