UK investigators are examining two incidents within an hour of each other in which landing aircraft of freight specialist Emerald Airways descended below terrain they had to cross on final approach.

Both British Aerospace BAe 748 twin-turboprops disappeared from radar while still some 7nm (13km) from the threshold of the Isle of Man runway off the north-west English coast - but eventually landed safely.

The crews were following the VOR/DME (distance measuring equipment) approach to runway 08 which is somewhat unusual in using a VOR/DME situated on the centreline, but 4.5nm out from the threshold, for guidance.

The effect of a similar type of approach is under examination as part of the investigation into the Korean Airlines Boeing 747-300 crash at Guam last year. It requires the pilot to count down the DME distance to the beacon and then up from the beacon to the threshold and is generally not liked by aircrew.

At the Isle of Man, the procedure calls for the VOR, which is virtually co-located with a 580ft hill, to be crossed at 1,430ft above sea level, during a steady descent on a constant heading to the threshold.

In the first of the incidents, on an unspecified day in June this year, the UK CAA says the aircraft "descended below profile following flap selection in moderate turbulence".

According to the initial CAA report, the aircraft's primary and secondary radar returns disappeared "between eight and six miles from the runway" and when contact was regained the aircraft was "allegedly at 300ft with a 580ft hill one mile ahead". The crew overshot and landed off a second approach.

The report does not state the cloudbase but a source familiar with the incidents says a substantial part of the approach was conducted in cloud.

The CAA says the pilot reported requiring an unusually high power setting, which was eventually restricted due to high turbine gas temperature, throughout the approach and suggests that there may have been windshear present.

By coincidence an official of the UK Air Accidents Investigation Branch (AAIB) was in the control tower throughout and observed what happened as well as a second incident which a pilot familiar with the events says occurred about 30min later - although that is not confirmed.

According to the initial CAA report of that incident, the aircraft positioned from the south and overshot the extended centreline partly because of a strong southerly wind.

Controllers alerted the pilot when they noted the aircraft's altitude as being only 700ft while still 7nm out and the aircraft then disappeared from radar. The aircraft climbed and was seen again on radar at 5.5nm "with a 580ft hill less than one mile ahead". It eventually landed from the approach. That investigation is also considering windshear as a factor.

Emerald Airways declines to comment while the AAIB investigation is underway.

The carrier is awaiting the final report on the loss of one of its 748s at London Stansted Airport in March this year which happened following an engine failure on take-off. There has been wide discussion of the actions of the pilot who successfully aborted the take-off apparently just after lift-off. There were no casualties.

Source: Flight International