Description

On 12 January 2011, a privately operated Socata TBM850 light aircraft on a flight from Antwerp to Birmingham lost radio contact with ATC whilst in Instrument Meteorological Conditions (IMC) on a non procedural approach to runway 15 prior to the issue of a landing clearance and prior to checking in on the ATC TWR frequency. It continued the approach to obtain the required visual reference before landing over the top of a DHC8-400 aircraft which had lined up ready for take off in accordance with ATC instructions. No damage or personal injury resulted from the close proximity.

Investigation

An Investigation into this Serious Incident was carried out by the UK AAIB. The incident aircraft was not required to be equipped with flight recorders, but the avionics system fitted recorded some flight parameters at one second intervals on an SD memory card which had retained details of the three flights flown on the day of the incident. Although this data was generally comprehensive, it did not include flap or landing gear selections, data relating to the integral Electronic Flight Bag or radio PTT activation. ATC recordings, including some Mode ‘S’ parameters and SMR, were available.

The Meteorological Terminal Air Report (METAR) current at the time of the incident included a wind direction and velocity (W/V) of 210° at 9 knots, a visibility of greater than 10 km in light rain and with cloud SCT / 600 feet and BKN / 900 feet. An NDB/DME approach had been in use for runway 15 at the time because the usual Instrument Landing System (ILS) was not available, although this was not being promulgated on the Automatic Terminal Information Service (ATIS) as required. It was established that the reason why the aircraft did not check in with TWR was because the pilot had mistakenly set 118.03 instead of the correct frequency 118.30. The original ATC intention had been to depart the DHC8 in between a previously landed Boeing 737 and the incident aircraft but the loss of contact created a situation in which the TWR controller had concluded that “there was no option that would allow the (DHC8) to depart or safely clear the runway and that holding it in its current location on the Runway 15 starter extension posed the least risk”.

Recorded data suggested that the pilot became visual with the runway at about 600 ft aal and at a range of about 1.3 nm from the threshold. The TWR controller assessed that touch down occurred abeam the Bravo intersection, about 270 metres from the displaced threshold and 170 metres prior to the TDZ. After vacating the runway, the pilot made contact with ATC GND on the same radio as had previously been used to attempt contact ATC TWR on the mis-set frequency.

It was apparent that the incident aircraft pilot had not noticed either his frequency selection error or the stationary aircraft on the runway. It was noted that the runway involved had a black-coloured asphalt surface with an landing distance available (LDA) of 2279 metres measured from the displaced landing threshold. Prior to this was a starter extension of 290 metres of which the first 160 metres had a “beige-coloured” concrete surface. The proximity of the two aircraft during the over flight is shown below:

It was noted that the incident aircraft pilot had relatively limited total flying experience, low experience on the aircraft type involved and last remembered flying an Non-Directional Beacon approach four years previously. It was considered by the Investigation that “low experience increases the probability of errors in skill and rule-based behaviour”. It was also noted that the pilot had probably been “subject to subtle pressures which may have reduced his probability of making good decisions” having flown three sectors over seven hours prior to the arrival at Birmingham with his three passengers being his employees and all due to attend the same business meeting as he was. It appeared to the Investigation that “plan continuation bias” had applied in respect of the continued approach.

In respect of the landing without clearance, it was considered that the normal presumption of air traffic controllers may be that a loss of communications with an aircraft established on the extended centreline of the landing runway will result in a go-around whereas pilots in that situation may expect to continue to a landing subject to no contrary indications or signals. It was felt that this disparity could lead to conflict between the controller and pilot mental models.

In respect of the option for visual signals to aircraft, it was noted that these had, with appropriate regulatory approval, been withdrawn from use but that there was no documented safety case to justify this action.

It was also noted that approximately three weeks prior to the investigated incident, NATS, the ANSP responsible for ATC at Birmingham, had issued a ‘Safety Notice’ entitled ‘Runway Safety - Landing without clearance’. Although titled ‘Safety Notice’ this had provided advice rather than presenting a mandatory operating instruction and due to administrative errors had been removed before some controllers, including the incident TWR controller, had seen it.

The formally-recorded Conclusions of the Investigation included the following:

• (High pilot workload during the NDB DME 15 approach) led to peripheral tasks being dropped and (the pilot’s) decision-making process being degraded. This led, without further fault diagnosis, to the misidentification of a frequency selection error as a radio failure. From that point on, the pilot’s actions from his perspective, although based on continuation bias, were in compliance with regulations. The same human factors that led to the misidentification of the radio problem probably also led to the failure of his visual search of the runway before he landed.

• The air traffic control procedures in use were compliant with the appropriate (requirements) and are standard practice throughout the UK. The controller’s planning assumption, supported by previous training, that aircraft should and probably will go around following a loss of communications, was widely shared throughout ATC management and the regulator. However, the controller’s plan provided little room for manoeuvre and included a single point, albeit unlikely, that could lead to it being disrupted.

• Following a loss of communications, ICAO Doc 4444 and the UK AIP require aircraft to continue visually and at least 17 multi-pilot public transport passenger flights have landed without clearance in the UK in the 12 months to March 2011. In those cases the runway was clear.

Various Safety Actions taken subsequent to the incident were noted and four Safety Recommendations were made:

• That the Civil Aviation Authority resolve the conflicting expectations of flight crews and air traffic controllers following a loss of communications during approach. (2011-073)

• That the Civil Aviation Authority review the risk assessment of the hazards associated with clearing aircraft to line up ahead of landing traffic. (2011-074)

• That (ANSP) NATS review the content of the Birmingham Airport Automated Terminal Information System to ensure that it is clear and concise, and includes the type of approach to be expected. (2011-075)

• That the Civil Aviation Authority review the most appropriate means of providing the visual instructions for which pilots are required to maintain a watch in accordance with Rule 45(6)(b) of the UK Air Navigation Order. (2011-076)

The Final Report of the Investigation AAIB Bulletin: 10/2011 EW/C2011/01/04 was published on 6 October 2011.

Further Reading

• Loss of Communication
• Communication Failure: Guidance for Controllers
• Expectation of Clearance
• Human Factors in AGC
• Communication Guide for General Aviation VFR Flights
• Loss of Separation - Pilot-induced Situations
• Runway Incursion
• Pilot Perception
• Pilot Workload
• Situational Awareness
• Pilot-Controller Communications (OGHFA BN)
• Press-on-itis and Inadequate Use of Automation (OGHFA SE)