UK airspace authority NATS is assessing options for providing timely alerts to air traffic controllers in the event that an aircraft descends significantly below its correct approach path.

NATS says it is investigating "various technology solutions" to determine whether controllers can be given appropriate warnings.

The organisation is responding to an inquiry by the UK Air Accidents Investigation Branch (AAIB), which has published findings into a serious low-approach incident at Manchester and is still investigating three other cases.

NATS says: "A key element of this investigative activity is ensuring that any alert is provided to the relevant controller - that is, the controller on frequency - in sufficient time for the controller to assimilate the information and issue appropriate instructions to the aircraft."

AAIB investigators are citing distraction and poor crew resource management as the reasons behind the dangerous descent of a EuroManx Dornier 328 turboprop, which flew below the glideslope while approaching Manchester airport in January.

On an instrument landing system approach to runway 24R, the aircraft descended to just 450ft (140m) while still 5.5nm (10.2km) from touchdown. Aircraft on a 3° glideslope would normally still be at 1,750ft at this point.

The aircraft had been arriving after a service from the Isle of Man on 18 January. The crew initiated a go-around after being alerted by the enhanced ground-proximity warning system. After a second ILS approach to the same runway, the aircraft landed safely, with no injuries to the 17 passengers and three crew members.

Air traffic controllers had cleared the 328 to descend from 3,000ft to 2,000ft, ahead of following the ILS. But while the descent was performed by the autopilot, the selected vertical speed was 1,500ft/min (7.62m/s) - a high rate of descent which resulted in the aircraft failing to capture the glideslope.

Despite the aircraft's dropping below its cleared altitude, and the rapid descent, the crew did not discuss the glideslope capture status. The turboprop came within 450ft of the ground in instrument meteorological conditions - a situation that "seriously compromised" the aircraft's safety.

"In the absence of any identifiable technical problem with the aircraft, it was considered that this resulted from the flightcrew not performing adequate 'cross-cockpit' monitoring, not applying cockpit resource management techniques and poor use of [standard operating procedures] throughout the flight," says the AAIB.

"While the crew noticed, initially, that they were below the glideslope, the aircraft continued with an excessive rate of descent and the range from touchdown was not checked against the associated heights on the approach plate," the AAIB adds. "The crew subsequently became distracted while configuring the aircraft for landing and trying to reduce their [airspeed]."

Source: Flight International