Landing on contaminated runway

Citation

(1999), "Landing on contaminated runway", Aircraft Engineering and Aerospace Technology, Vol. 71 No. 4. https://doi.org/10.1108/aeat.1999.12771dab.018

Landing on contaminated runway

Landing on contaminated runway

Keywords: Aircraft, Landing, Runway, Safety

A BAe 146 aircraft and crew were planned to operate a scheduled passenger flight from London Gatwick to Belfast City Airport (Figure 1). The First Officer (FO) was the handling pilot for the flight. He had 3,743 hours' experience on this type of aircraft. As the aircraft approached the top of descent point for Belfast City the flight crew obtained the latest Automatic Terminal Information Service (ATIS) which reported surface wind 060ú/06 knots, visibility 5,000 metres in rain, cloud scattered at 600 feet and overcast at 1,100 feet. The surface temperature and dew point were coincident at +13úC and the QNH was 1,003mb. The ATIS also identified Runway 22 as the runway in use for landing aircraft. This runway has a concrete surface with an available landing distance of 1,750 metres. The runway is served by high intensity approach lights, threshold and stop end lighting and runway edge lighting, the PAPIs are set to 3ú and all lighting was serviceable.

Figure 1 Selected parameters from the approach and landing at Belfast

The crew contacted Belfast approach at 18.00hrs and were given radar vectors for the ILS to Runway 22. The aircraft was established on the localiser at 10n n miles from touchdown at an altitude of 1,700 feet and was handed over to the tower frequency at 18.05hrs. On initial contact with the tower frequency the controller passed the current surface wind of 040ú/07 knots and the runway state as ''wet with water patches''; this transmission was acknowledged by the crew. At this stage the FO questioned the wisdom of continuing the approach to land given the combination of a tailwind and water on the runway; however the commander elected to continue. At 18.07hrs the aircraft was cleared to land and passed the current surface wind of 060ú/10 knots. This surface wind was subsequently updated to 080ú/10 knots and then 070ú/12 knots by the tower controller during the remainder of the approach. These later wind velocities equate to a tailwind component of eight knots and ten knots respectively when using Runway 22.

The crew could see the runway lighting, including the PAPIs, from glideslope intercept at 1,700 feet and the approach was stabilised on the glideslope throughout. At about 500 feet the indicated airspeed was 12 to 14 knots greater than the required approach speed of 122 knots. This discrepancy was corrected by the use of speedbrake and by about 300 feet the crew were satisfied that the airspeed was now at the correct value. At the ''10 feet'' radio altimeter call the commander assessed that the aircraft was directly above the touchdown zone markers and the PAPIs were changing from two red and two white lights to one red and three white lights. The FO initiated the flare but the aircraft did not contact the runway and continued to float. After a short time the commander told the FO to place the aircraft on the runway and nudged the control column forward to ensure ground contact. Once on the ground the commander selected the spoilers whilst the FO commenced braking. After a further short period of time the commander also began braking and applied maximum pressure to the brake pedals.

He became aware that the remaining runway appeared to be covered in standing water and believed that aquaplaning occurred as he continued to apply maximum braking pressure. As the aircraft approached the threshold of Runway 04 the commander realised that the aircraft was not going to stop, so he used the nosewheel steering to turn to the left in an attempt to vacate the runway by the taxiway. The aircraft went off the end of the runway and came to a halt on a heading almost 90ú to the runway centerline and embedded in the mud about seven metres from the runway surface. The commander realised that the aircraft was undamaged and confirmed with the cabin supervisor that there were no injuries to the passengers. He therefore decided not to initiate an emergency evacuation but instead commenced the normal shutdown checklist.

As soon as the tower controller realised that the aircraft had left the runway surface he sounded the crash alarm and the airfield fire and rescue services responded immediately. When they arrived at the aircraft the commander spoke to the fire chief through the direct vision (DV) window and requested steps to be made available to allow disembarkation of the passengers. Fire and ambulance services from off the airfield also attended at the scene and remained available until all of the passengers had been moved to the passenger terminal and the aircraft had been handed over to the local aircraft engineers who organised the subsequent recovery of the aircraft.

Technical examination and runway details

The tyre marks on the runway showed that as the aircraft entered the loop at the threshold end of Runway 04 an attempt had been made to turn to the left; this was unsuccessful and the aircraft rolled onto the grassed overrun area and came to rest approximately seven metres beyond the paved area. Whilst the tyres showed abrasions produced by the sideslip they had experienced before leaving the runway, there were no indications of scald marks or rubber reversion normally associated with aquaplaning.

Subsequent checks showed that the Yellow and Green hydraulic system pressures, and the aircraft main and nosewheel tyre pressures were satisfactory. A functional check of the ASIs against calibrated test equipment showed no discrepancies up to 130 knots, and a maximum of four knots discrepancy between 130 knots and 180 knots. Brake pressure tests and an anti-skid functional test were carried out with no faults found.

The aircraft did not carry any relevant Acceptable Deferred Defects, and the technical log had no brake, anti-skid, ASI or spoiler defects reported in the previous three months.

Runway 22 is the preferred landing runway at Belfast City whilst Runway 04 is the preferred departure runway. From the point of view of glideslope origin on the runway surface, as defined by both the ILS glideslope and the PAPIs, 1,509 metres of runway length is available for Runway 22. The runway width is 66 metres which is considerably wider than the runways at all other scheduled destinations for this operator which have runways that are 45 to 46 metres wide. The runway is surfaced with large concrete blocks with a rubberised sealant between the blocks. In any heavy precipitation there is the possibility of water pooling in these blocks if there is any misalignment between them. This was seen to occur the day after the accident following some heavy rain showers and may explain the commander's perception of extensive areas of standing water during the landing rollout.

A runway friction classification of this runway had been performed on 29 January 1998. The average readings for the runway were well above the maintenance planning requirements (average 0.75, maintenance planning level 0.63). It was noted during this friction classification that whilst the runway generally had good high speed friction qualities there was a marked deterioration when crossing the painted touchdown zone markers which are displaced 10.5 metres from the runway centreline. It was recommended that action to improve the readings on these painted surfaces should be considered. Rubber deposits were described as light in the touchdown area of Runway 04.

ATIS had informed the pilot that the runway state was "wet with water patches" and this transmission was acknowledged by the crew. The Manual of Air Traffic Services Part I, Section 9-3, Chapter 2 defines the manner in which water on a runway is to be reported. The information passed to the crew on this occasion is issued "When the surface is soaked and significant patches of standing water are visible".

Procedures and summary

Landing on contaminated runways is discussed in Part 9, Section 4, Chapter 9 of the company's Operations Manual where a runway is described as contaminated "when more than 25 per cent of the length and width to be used is covered with ice, standing water, slush or wet snow to a depth exceeding 3mm". The maximum permitted tailwind for operations on such a runway is defined as five knots. Furthermore, when landing on a contaminated runway the pilot is required to plan and execute the approach and landing as for a "short field" landing. This initially requires the maintenance of a normal glideslope at an airspeed of Vref + 5 knots, then, during the final stages of the approach the speed brake should be extended and speed reduced to cross the threshold at Vref at a height of about 30 feet. The pilot should then aim to touchdown in the first 500 feet of the runway and is specifically warned not to let the aircraft float.

In summary, the flight crew accepted the preferred runway, Runway 22 as their landing runway despite the reported tailwind. Landing on this runway was their normal routine and their published landing figures allowed for a landing with a ten knots tailwind on a wet surface. Even after the FO expressed doubts about the tailwind the commander was satisfied that it was safe to continue the landing for Runway 22.

ATC had informed the pilot that the runway was "wet with water patches" because the runway surface was soaked and significant patches of standing water were visible. ATC therefore expected that the pilots would realise that wheel braking and control might be affected by aquaplaning since this information is available in the UK Aeronautical Information Publications (AIP). However, the crew were unaware of the implications of this description of the runway surface since the definition of a contaminated runway published in their Operations Manual specifies "more than 25 per cent of the length and width to be used is covered with ... standing water ... to a depth exceeding 3 mm''. Therefore, the crew did not consider that they were approaching a contaminated runway and did not apply the associated limiting tailwind of five knots nor did they brief for the short field landing technique.

As the result of a number of incidents which have occurred to aircraft when landing on wet or contaminated runways the CAA believed that there was a need to further enhance the consistency of information relating to the various classifications of runway surfaces; the aim being to ensure that both air traffic controllers and pilots have access to the same information. The CAA is currently producing an AIC on this subject; there will also be an associated amendment to the AIP.

Once landing flap of 33ú had been selected at 750 feet the aircraft was stabilised at a speed of 130 KIAS for the remainder of the approach and at 35 feet it was at 128 KIAS. At the estimated landing weight the correct approach speed was 122 knots (Vref + 5 knots) with the associated speed at the threshold of 117 knots. The landing performance for this aircraft is predicted upon achieving an accurate speed schedule during the approach and landing. It is therefore imperative that flight crews ensure that this speed schedule is followed when making an approach to land on a limiting runway.

Once established in the flare the handling pilot did not place the aircraft on the ground but allowed it to float until prompted, both physically and verbally, by the commander. This misjudged flare may have been caused by the handling pilot misinterpreting the visual clues provided by the unusually wide runway. The error was exacerbated by the ten knots tailwind.

The aircraft finally touched down with approximately 968 metres of runway remaining at an indicated airspeed of 111 knots with a 10 knots tailwind and on a surface that was wet with water patches. During the braking there was no evidence, from the physical examination of the tyres, of any aquaplaning. The performance of the aircraft during the ground roll, with the spoilers extended and maximum braking applied, was as expected on a surface that was wet with standing water.

Reference: AAIB Bulletin 3/99.