Van L410 at Belfast and Isle of Man on Feb 23th 2017, weather related diversion and exceedance of cross wind limits during taxi results in grounding of airline
Last Update: March 8, 2018 / 16:22:41 GMT/Zulu time
The prime causal factor in this serious incident was the decision to land with a maximum crosswind component of 40 kt, which is approximately twice the maximum demonstrated certification value of 19.4 kt. In the view of the aircraft operator, there was no specific crosswind limit the crew needed to consider when deciding whether to operate the service or not. However, the OM Part A refers to a crosswind limit when it states: ‘For planning purposes an aerodrome shall be considered below minimum if the steady crosswind exceeds the prescribed limitations.’ and other evidence from the AFM and the OM indicates that the maximum demonstrated crosswind component of 19.4 kt was limiting.
Several contributory factors were also apparent:
1) By only studying weather reports for six airfields and without referring to any meteorology charts, the crew had insufficient information to assess the prevailing weather conditions en route and the storm’s path.
2) The aircraft operator believed that a valid TAF could be disregarded upon the subsequent issue of a METAR that included a TREND forecast.
3) The aircraft operator did not provide adequate oversight to a flight in airspace affected by this storm. The commander did not refer to the available weather forecast charts and neither the OCC nor the FOM reviewed the situation with him, or suggested he seek guidance from the duty forecaster.
4) The fuel figures presented on the OFP did not account for the correct level of contingency fuel and did not allow for a realistic alternate routing. The aircraft had sufficient fuel for the sector, but the crew did not have as much extra fuel on-board as they believed they had, and the OM offered little guidance on the carriage of extra fuel when there was a possibility of widespread, adverse weather conditions.
5) The OFP only showed navigational and fuel information for the second of two selected alternates. However, the two Belfast airports are in close proximity so the lack of navigational information for the routing to the first alternate may not have been problematic in this instance.
6) The CVR evidence, that evolving threats did not precipitate verbal discussion between the pilots, indicates they had not been effectively trained in respect to CRM, and to threat management in particular. The OM appeared to lack guidance concerning the evaluation and management of threats, problem solving and decision making.
7) The approach became unstable before visual flight conditions were achieved, but the crew did not discuss this, and the required SOPs were not followed.
8) The limiting airspeed for flight with gear down and for flight with flaps extended was exceeded but no corrective action was taken.
9) The crew began taxiing the aircraft in a wind which was stronger than the wind which blew a similar aircraft onto its wingtip at IOM in 2007 and which exceeded the ground operation limit introduced after the 2007 accident.
The AAIB described the events at Belfast:
No difficulties were encountered en route to BHD, and the PNF listened to the 0827 hrs Automatic Terminal Information Service (ATIS). This stated that Runway 22 was in use and quoted the 0820 hrs METAR3, with the wind orientated across the runway at 25 G 40 kt. When the PNF contacted BHD ATC, he was told radar vectoring was available for an ILS approach to Runway 04 and that the wind was now from 320º at 28 G 43 kt. The PNF informed ATC they would make one approach but would go around if the approach was not stable.
The crew reported afterwards that they experienced continuous moderate turbulence during the latter part of the approach. The final wind check, given after they had been cleared to land, was from 320º at 35 kt. They judged that the aircraft operator’s stable approach criteria4 were met until the aircraft passed over the runway threshold, when turbulence de‑stabilised the aircraft and they initiated a go-around.
ATC reported that the aircraft went around from approximately 20 ft above the runway at 0858 hrs and climbed straight ahead to 3,000 ft amsl, the standard missed approach procedure. The aircraft continued heading northeast until 0901 hrs when the PNF informed ATC they would not make a second approach and would return to IOM.
The AAIB described the sequence of events on approach and landing following the return to Isle of Man:
At 0913 hrs, the PNF informed the PF there was about 300 kg of fuel remaining and this was enough “for one more hour”. Without further discussion, the crew accepted radar vectoring for an ILS approach to Runway 26, with the co-pilot remaining as PF. Before the aircraft was directed towards its final approach, ATC reported the wind was from 310º at 43 kt but gusting between 23 and 63 kt.
At 0924 hrs, after the aircraft had become established on the ILS centreline and glideslope, ATC radioed clearance to land, with a reported wind of 300º at 41 kt but gusting between 31 and 63 kt. While receiving this message, the crew were also presented with an aural “glideslope” caution and immediately after this the PF declared “1,000 ft stabilised”. At 0925 hrs, while the PNF was adjusting the propeller rpm, another aural “glideslope” caution was annunciated and the PF immediately stated “correcting”. At 0926 hrs, following an automatically generated message stating the aircraft was at 500 ft agl, one further “glideslope” caution was annunciated and the PF responded saying “correcting, runway in sight”.
The final wind check provided by ATC, approximately 35 seconds before the aircraft touched down, was from 300º at 48 kt, but gusting between 32 kt and 63 kt. The commander reported afterwards that the runway was in sight at 600 ft.
Given the environmental conditions, ATC was concerned for the safety of the aircraft and its occupants when it landed, so the airfield Rescue and Fire Fighting Service (RFFS) had been placed on alert with two vehicles facing towards the runway, approximately 200 m from the touchdown zone. During the aircraft’s approach, ATC discussed the situation with the Isle of Man Civil Aviation Administration because another of the same operator’s aircraft had been blown onto its wingtip while taxiing in 200710, in winds greater than 45 kt, and both parties knew 45 kt was now the operator’s maximum ground operation limit.
Four RFFS and two ATC witnesses reported that as the aircraft crossed the threshold it seemed unstable and it rolled considerably, causing the tip of the left wing (the downwind wing) to tilt down until it seemed in close proximity to the runway, before the wheels made first contact. The aircraft then bounced and rolled left again before touching down for a second time, on all three wheels.
After travelling along the runway for approximately 20 m, the right mainwheel was seen to lift off the ground and nearby RFFS witnesses estimated the left wingtip rolled to within one metre of the runway surface. The crew seemed aware of this roll because, approximately nine seconds after touchdown, the PF stated “ailerons…good…too much roll”. The commander stated afterwards that he thought all the wheels remained on the ground and that the aircraft responded to appropriate aileron control; he had no concern that the wingtip or the propeller might have been close to the ground.
After landing the commander took control and the co-pilot commented “taxi carefully with the wind”. ATC then stated the surface wind was from 300º at 47 kt, but gusting between 32 kt and 63 kt and asked if they wished to taxi or to hold on the runway. The crew replied “we will try and taxi and if we can make it we will vacate, otherwise we need to leave the aircraft here”. The crew then accepted taxi instructions directing them towards the terminal but, 45 seconds later, as the aircraft was leaving the runway, ATC radioed to the crew, “direction from Isle of Man CAA, hold position.” The aircraft stopped facing into the wind.
Both ATC and the Isle of Man Civil Aviation Administration later indicated that they were concerned that if the aircraft continued to taxi with the wind gusting to 63 kt an accident could occur. The Isle of Man Civil Aviation Administration therefore issued a directive11 that the aircraft be held in its current position and it was subsequently shutdown into wind near the junction of Runway 26 and Taxiway C, with 220 kg of remaining fuel being recorded.
RFFS vehicles were positioned around the aircraft, to provide some screening from the wind, and a bus transferred the three uninjured passengers to the terminal building. The aircraft was later tied down until the wind subsided.
The AAIB analysed that the Isle of Man is a UK Crown Dependency but is not member of the European Union (other than the UK itself). The Isle of Man therefore have their own Civil Aviation Authority to ensure air safety on the island and wrote: "It is an Isle of Man requirement that aircraft registered in a foreign country obtain a Foreign Carrier Permit to operate commercial flights to or from the Island, while the UK has to provide a permit for commercial flights to or from the UK from a non-EU Member State. Consequently, the administration of Foreign Carrier Permits for commercial flights between the UK and the Isle of Man is delivered by the UK CAA in co-ordination with the Isle of Man Civil Aviation Administration. This operator had been issued with such a permit for its operation between the Isle of Man and the UK on behalf of the ticket-selling company."
The AAIB continued that following a number of operational incidents a joint oversight of both Czech's CAA and UK's CAA was agreed. THe AAIB then wrote:
The UK CAA stated that its joint oversight with the CAA of the Czech Republic identified shortcomings in management structure, operational procedures and in the way the operator’s crew were trained, particularly in threat and error management principles. Although the oversight trial was completed once a programme to address these deficiencies had been agreed, the two NAAs continued to work together to secure further safety and compliance improvements by the operator. To retain its Foreign Carrier Permit the operator had to submit monthly updates and consequently the UK CAA learnt that the newly appointed FOM lacked, in its view, the appropriate experience, knowledge and authority to hold this post, while his deputy also had very little operational experience.
On 22 February 2017, representatives of the UK CAA met their Czech counterparts and requested that inspectors from the two NAAs perform a cooperative audit of the operator at IOM to confirm that safe operations could be guaranteed by the new management structure. The next day this serious incident occurred and, after informing the CAA of the Czech Republic, the UK CAA suspended the Foreign Carrier Permit and issued a Direction under the UK Air Navigation Order, instructing the operator to suspend UK Commercial Air Transport operations indefinitely.
Both NAAs agreed that a crosswind limit of 19.4 kt should have been applied for takeoff and landing. The CAA of the Czech Republic also stated this was the limit that was accounted for when the pilots’ type ratings were issued and it also noted the ground operation limit related to aircraft taxiing and was not a takeoff and landing limit.
The AAIB analysed that the operator had done their own initial investigation and provided a report of their investigation to the AAIB. The AAIB wrote:
The report considered whether more fuel might have been carried, but noted that the operator’s guidance to the crew for such circumstances was lacking. Having elected to fly an approach at BHD, the report endorsed the crew’s decision to go around but indicated that with a relatively low fuel state, BFS might have been a better airport to divert to. Once en route to IOM, the wind at the surface increased above the operator’s ground limit but the crew were committed to continuing due to the fuel state. However, the report acknowledged they could have declared a fuel emergency (an intention to land with less than final reserve fuel) and proceed to another suitable airport, such as Blackpool.
Because the operator’s opinion was that the demonstrated crosswind figure was not limiting, the report concluded that the ‘operation was legal’, except for landing in a wind beyond the ground operation limit. It commended the piloting skills that led to a ‘safe landing’.
The final report concluded that the crew’s final decision to land at IOM was ‘reasonable’ but indicated there were deficiencies in threat and error management which required safety action.
The AAIB quoted two prior occurrences in their analysis:
OK-UBA, Let L-410, IOM, 18 January 2007
While taxiing at IOM, with a wind velocity from 260º at 37 G 57 kt, the right wing lifted and the left wingtip struck the ground, causing damage to the wingtip fuel tank. This was investigated by the AAIB and reported in Bulletin 8/2007. The aircraft operator subsequently imposed a maximum wind limit for ground operation.
IOM ATC Report, 30 December 2015
A Mandatory Occurrence Report (MOR) was submitted to the Isle of Man Civil Aviation Administration after another of the aircraft operator’s Let L-410s landed on Runway 21 when the reported wind velocity was from 210º at 45 G 65 kt. After landing the pilot shutdown the aircraft on a taxiway because of the strong wind. ATC filed the MOR knowing (from the AAIB’s 2007 report) that a maximum wind limit of 45 kt applied for ground operation and because of concern for the safety of those on-board, while disembarking on an exposed taxiway in 65 kt gusts of wind.
The AAIB analysed with respect to demonstrated cross wind handling:
The OM included the statement that with a 20 kt crosswind during takeoff ‘lateral controllability on the ground was close to being limiting.’ Indeed, the OM contained no other guidance concerning handling the aircraft during crosswind takeoff and landings, nor concerning the value of crosswind gust factor to be taken into account when calculating the crosswind, nor was there any recommendation concerning circumstances in which the maximum demonstrated crosswind might be exceeded. Additionally, the CAA of the Czech Republic stated that the maximum value of crosswind component accounted for when the pilots’ type ratings were issued was the maximum demonstrated component (19.4 kt).
The SOP was for the ground operation limit to be applied to determine if an airfield was useable or not, even though this limit should only have applied to taxiing manoeuvres. Moreover, the guidance in the OM that an airfield is to be considered as ‘below minimum’ at the planning stage if the steady crosswind exceeds the ‘prescribed limitations’, was not followed. Before takeoff, the IOM forecast, covering the period the aircraft might have had to divert back there, was for the surface wind to be from 310º at 33 G46 kt, meaning the crew should have assumed a crosswind component of 25 kt (disregarding the forecast gusts).
The AAIB analysed the decision to return to Isle of Man:
The aircraft took off from IOM with a crosswind component of 20 kt and later made an approach to BHD in a crosswind that was gusting to 43 kt. Continuous moderate turbulence was experienced during the approach and at all times the reported wind significantly exceeded the maximum demonstrated crosswind component by a significant margin. The conditions were such that usually it would be expected that a go-around be initiated earlierthan the reported height of approximately 20 ft above the runway.
Although the crew stated afterwards that they considered BFS to be their primary alternate airfield, they did not ask ATC for an update on the BFS weather before heading back towards IOM. This indicates that either they did not fully appreciate the synoptic situation, with the wind at IOM likely to veer and increase above that experienced on departure (as forecast by the TAF), or that they were too focussed on IOM as their preferred alternate airfield.
The commander’s statement after the flight that he considered the winds at BFS and IOM to be “similar” indicates that he did not give due consideration to the orientation of the runways.
The mean wind forecast at BFS was 33 kt and aligned close to the axis of an available runway, while the mean wind forecast at IOM was of a similar strength but from 50º right of an available runway orientation. Also, BFS was the airfield the crew said was their planned primary alternate, as well as being the ticket-seller’s preferred commercial alternate, and the mean wind there was not forecast to exceed the aircraft operator’s ground limit.
The crew’s focus on returning to IOM indicates they formed a mental or cognitive bias towards returning there after deciding to show it as the only alternate airfield on the OFP.
The AAIB analysed the arrival at Isle of Man:
There was credible witness evidence that the aircraft rolled considerably as it approached the runway and that the right mainwheel lifted off the ground after touchdown, causing the left wingtip to roll to within one metre of the runway surface. The crew did not know the wheel lifted or observe the ground clearance of the wingtip but the co-pilot was sufficiently concerned to state ‘too much roll’. It is therefore apparent that lateral control difficulties were experienced while landing due to the very strong, gusting crosswind.
Immediately after landing, the crew began to taxi the aircraft in a wind which exceeded the ground operation limit of 45 kt; the steady wind speed was 47 kt and with the addition of half of the gust factor the total applicable wind was 55 kt. This suggests the crew were not fully aware of the risk that the lightly loaded aircraft might be blown onto its wingtip, even though this had happened to another of the same operator’s aircraft at IOM in 2007, in lighter winds. IOM ATC and the IOM Civil Aviation Administration knew about the previous accident and were concerned for the safety of those on board this aircraft.
The aircraft required ATC permission to taxi on the manoeuvring area and this permission was withdrawn when ATC passed on the directive from the IOM Civil Aviation Administration, which brought the aircraft to a halt into wind. The aerodrome controller has authority over an aircraft on the ground and although the directive from the IOM Civil Aviation Administration for the aircraft to cease taxiing may be unusual, it was apparently made with the aim of preventing an accident.
This article is published under license from Avherald.com. © of text by Avherald.com.
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