Wideroe DH8A at Sandnessjoen on Sep 15th 2010, main gear collapse on landing
Last Update: July 7, 2015 / 17:13:13 GMT/Zulu time
Incident Facts
Date of incident
Sep 15, 2010
Classification
Accident
Airline
Wideroe Airlines
Flight number
WF-701
Departure
Bodo, Norway
Destination
Sandnessjoen, Norway
Aircraft Registration
LN-WIF
Aircraft Type
De Havilland Dash 8 (100)
ICAO Type Designator
DH8A
The airline said in their press release, that the airplane touched down so hard that parts of the landing gear collapsed. A spokesman for the airline explained, that the airplane caught a gust during flare which caused the airplane to touch down that hard. He later went on saying, that Sandnessjoen is notorious for downdrafts due to the nearby mountain range, the wind conditions today however were not particularly difficult and the winds were far below all limits, basically just normal.
One of the pilots had recently joined Wideroe and was under supervision with an instructor occupying the observer's seat.
Norway's Havarikommission have dispatched three investigators to Sandnessjoen.
The landing gear assemblies of the Dash 8-100/200/300 are produced by different manufacturers than the assemblies for the Dash 8-400/Q400. The landing gear of the -100/200/300 have a "fusible link pin" that is designed to shear after a hard landing to protect a possible main landing gear leg from being driven up and into critical components in the nacelle and wing area. The pin would typically shear at touch down with a vertical speed above 14 feet per second/840 feet per minute.
On Jul 7th 2015, almost 5 years after the occurrence, Norway's AIBN released their final report in Norwegian (including English summary) concluding the probable cause of the accident was:
- The AIBN looked at the various operational and technical aspects, each of which was within applicable limits. The combination of approach angle, limited experience on the aircraft and sudden wind change caused a hard landing.
- the wind change just before touch down came so quickly that AFIS could not broadcast the change
- during touchdown the combination of horizontal and vertical forces on the right main landing gear exceeded the value that the aircraft manufacturer had designed the safety bolt to separate at. This resulted in the collapse of the right main gear.
The AIBN reported that the pilot in command (Wideroe's chief pilot, 57, ATPL, 9,090 hours total, 3,015 hours on type) was occupying the right hand seat and assumed the role as pilot monitoring while acting as instructor for the captain candidate (50, ATPL, 10,141 hours total, 11 hours on type) occupying the left hand seat and assuming the role as pilot flying. The captain candidate had previously flown MD-80s as first officer, Fokker 50 as captain, then A330 for 7 years as first officer and Boeing 737s for two years. He joined Wideroe in 2010, went through the Dash 8 type conversion course combined with the command course. Prior to the accident he had flown 6 landings and conducted line training. Sep 15th 2010 was the third day of his line training. Following the accident he continued the routine training and was checked as Dash 8 captain in March 2011.
The AIBN reported that before the approach to Sandnessjoen's runway 03 the crew briefed the company wind limits for the approach, which permitted a maximum wind limit of 15 knots in the sector from 060 to 150 degrees, this limit had been set by the operator due to high terrain east of the aerodrome and difficult landings with winds down from the mountains. AFIS provided wind information three times during the approach, each of which was within company limits with winds between 9 and 15 knots.
In the English summary the AIBN wrote: "In a very short time the wind gusting up to 17 kt. The AFIS officer was about to grab the microphone and inform WIF701, but this was too late because he saw the aircraft was about to touch down. At the same time as the radio altimeter announced 20 ft, the pilots experienced a significant increased descend. The captain candidate decided to do an aborted landing and was about to increase power, when the aircraft hit the ground. The landing was heavy and the right main gear collapsed with the result that the aircraft settled down on its side. Despite this, the pilots managed to keep the aircraft on the runway. After the aircraft had come to a complete stop, an evacuation was initiated. The fire brigade arrived at the aircraft very quickly. No persons were injured."
In the Norwegian detailed factual description of the landing the AIBN reported that both pilots felt everything was normal until the aircraft descended through 50 feet AGL, only the GPWS automatic call outs 100, 50, 40, 30, 20 were heard in the cockpit at that time, at 50 feet AGL the engine torque was at about 20%. At 50 feet the pilot flying felt as if the aircraft was descending and became unstable as result of the wind changing direction to a tail wind and decided to go-around. He pushed the power levers forward to about 75% torque, but at that point the aircraft impacted the runway about 3 seconds after the 50 feet GPWS call out. The engines accelerated only after the aircraft had impacted ground, the aircraft had rotated to about 5 degrees nose up at the time of ground contact, the aircraft's heading was about 5 degrees right of the runway center line's heading. Immediately after first contact with the ground the right gear collapsed and the right wing contacted the runway surface. The captain's candidate retarted the thrust levers after impact and worked to keep the aircraft on the runway.
AFIS saw the right main gear collapse and activated the crash alarm instantly.
Neither pilot perceived the landing as particularly hard. The instructor thought that the aircraft may have skidded slightly sideways upon ground contact (de-crabbing).
Post occurrence examination revealed substantial damage to the right main gear, the right engine and propeller and the underside of the fuselage. The right main gear's fuse pin had sheared off causing the collapse of the gear. Part of a propeller blade had impacted a passenger window but had not penetrated the cabin.
The AIBN analysed that the captain candidate had solid flying experience, had undergone type conversion and passed the skill test required by the Aviation Authority, had conducted landings and was found ready for line training by the operator. The AIBN considers the captain candidate was adequately trained to carry out the flight operated that day. The commander/instructor had solid plane and instructor experience on the Dash 8. In addition he was well acquainted with the challening wind conditions at Sandnessjoen.
The AIBN further analysed that a pilot with more experience on type probably could have dealt better with the sudden wind change on short final. However, the AIBN does not believe it was necessary for the instructor at any time to take over control of the aircraft.
The AIBN analysed that at the time of the accident a wind monitoring system had not been installed at Sandnessjoen, which would have been benefitial and possibly could have averted the accident. Such a system was installed following the accident.
The AIBN analysed that with the limited experience of the captain's candidate it would have been more prudent to allow for a longer final, which would have permitted the pilot flying some more time to adjust to the aircraft in the present wind conditions. However, a longer final leads to less comfort for passengers which is why Wideroe recommded short final legs.
The AIBN analysed that the approach was still stabilized at 150 feet AGL, at that point a wind of 7 knots from the right prevailed. Below 150 feet the wind increased to about 17-18 knots in the last seconds just before touch down.
The AIBN analysed that both pilots showed good crew cooperation carrying out their tasks professionally.
The AIBN analysed that the captain's candidate following the stop of the aircraft decided to evacuate the aircraft, the evacuation order however did not reach the aircraft's speaker system. The captain in command and instructor considered an evacuation was not necessary. This had no practical consequence in the accident, the operator however improved the check list "Emergency on the ground" to address the issue.
The AIBN analysed that in order to permit Dash 8-100s and Dash 8-200s land on runways of 800 meters length, it was needed to equip the aerodromes with 4.5 degrees glidepathes. The AIBN considers that the short runway contributed to the accident to a small extent, but the steep glide angle contributed to the accident to a significant extent. Steep approach angles provide for a large vertical energy of the aircraft and provide for a smaller window of timing to flare the aircraft. The fact that the runway was lengthened by 300 meters in 2014, with the glide path still at 4.5 degrees, did not change the probability of a hard landing.
The AIBN analysed that the right main gear fuse pin had been manufactured to specification and broke as result of overload as designed.
The AIBN analysed that the aircraft contacted ground at a vertical rate of descent of 16 feet/second (960 fpm) resulting in a vertical acceleration of +2.83G, experiencing lateral skid forces of 0.65G at the same time. This resulted in a force generated at the fuse pin in excess of its design load. The manufacturer recommendation was that the fuse pin should shear at a rate of descent between 14.9 and 17.15 feet/second.
The AIBN analysed that whenever a gear collapses there is a possibility that fragments of the propeller separate and impact the fuselage. If the energy of the fragment is sufficiently large there is danger that the fragment could penetrate into the cabin and injure persons on board of the aircraft. The AIBN wrote: "The issue is considered known to the industry."
The AIBN analysed that the investigation had access to the results of Wideroe's internal investigation. The Accident Investigation did not find any recommendations to be promoted beyond the measures already taken by Wideroe as result of the internal investigation's recommendations.
Metars:
NST 150650Z 11010KT 040V160 9999 VCSH FEW030 BKN040 14/09 Q0982
ENST 150550Z VRB06KT 9999 FEW030 SCT040 14/09 Q0982
ENST 150350Z 04007KT 360V140 9999 -RA VCFG FEW035 BKN060 14/10 Q0982
ENST 150250Z 02007KT 330V090 9999 CAVOK 14/09 Q0983
ENST 141850Z 01003KT 330V120 9999 -RA FEW020 SCT030 BKN050 12/10 Q0990
Aircraft Registration Data
Incident Facts
Date of incident
Sep 15, 2010
Classification
Accident
Airline
Wideroe Airlines
Flight number
WF-701
Departure
Bodo, Norway
Destination
Sandnessjoen, Norway
Aircraft Registration
LN-WIF
Aircraft Type
De Havilland Dash 8 (100)
ICAO Type Designator
DH8A
This article is published under license from Avherald.com. © of text by Avherald.com.
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