LOT DH8D at Warsaw on Jan 10th 2018, nose gear did not extend on landing

Last Update: January 17, 2020 / 16:56:58 GMT/Zulu time

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Photo of LOT Polish Airlines SP-EQG, De Havilland Dash 8 (400) — LOT Polish Airlines SP-EQG, De Havilland Dash 8 (400) (Photo credit: Bartlomiej Mostek / Flickr / License: CC by)

Incident Facts

Date of incident
Jan 10, 2018

Classification
Accident

Airline
LOT Polish Airlines

Flight number
LO-3924

Departure
Krakow, Poland

Destination
Warsaw, Poland

Aircraft Registration
SP-EQG

Aircraft Type
De Havilland Dash 8 (400)

ICAO Type Designator
DH8D

A LOT Polish Airlines de Havilland Dash 8-400, registration SP-EQG performing flight LO-3924 from Krakow to Warsaw (Poland) with 59 passengers and 4 crew, was climbing out of Krakow when the crew spotted a problem with the nose gear, stopped the climb at FL100 and turned to return to Krakow, but then decided to continue to Warsaw, climbed the aircraft to FL140. In contact with Warsaw approach the crew indicated they intended a full stop landing on runway 11 right away, no low approach was intended, subsequently on approach to runway 11 the crew indicated they had an unsafe nose gear indication, the gear likely did not extend, an alternate gear extension had already been carried out. The aircraft positioned for an approach to runway 11, the crew reported they were 100% sure that the "nose wheels did not come out", they had both main gear but no nose gear, they had checked it twice. The aircraft landed on runway 11 and came to a stop on both main gear and the nose of the aircraft. There were no injuries, the aircraft sustained substantial damage.

The runway and airport was closed.

The airport reported the aerodrome was closed for estimated 4 hours following an emergency landing by a LOT aircraft. Rescue operations were in progress.

The airline reported the nose gear did not lock, after landing the nose gear collapsed and the nose of the aircraft hit the runway.

Poland's PKBWL have opened an investigation into the occurrence.

On Jan 15th 2018 Transport Canada released Airworthiness Directive CF-2018-01 reporting: "A landing incident took place whereby the aeroplane’s nose landing gear (NLG) was locked in a partially-extended position, leading to gear collapse upon NLG touch down. The investigation revealed that the NLG was locked in this position due to the bushings on the lock link of the NLG locking mechanism becoming loose. This condition was present due to insufficient interference fit which resulted in some bushing outer diameter wear and fretting. A dislodged bushing will also cause the bushing sealant to break. Broken sealant allows moisture ingress and corrosion that can accelerate free play buildup. Excessive free play at the lock link can result in the inability to fully retract or deploy the NLG, resulting in a risk of NLG collapse on landing." The AD requires operators to comply with Bombardier's Service Bulletin (SB) 84-32-153, dated 22 September 2017 (or later), within 800 flight cycles if the nose landing gear accumulated more than 7200 flight cycles total/before 8000 flight cycles total if the nose landing accumulated less than 7200 flight cycles. Subsequently the nose landing gear is to be inspected every 1600 flight cycles according to SB 84-32-153.

On Jan 16th 2020 the PKBWL released an interim statement in Polish stating that after the gear was selected up, the nose gear remained in an intermediate position between gear down and gear up, the nose gear doors remained open. The captain decided to continue to Warsaw nonetheless, on approach to Warsaw the crew performed an alternate gear extension, which released the main gear into their down locked positions, the nose gear however did not move. The aircraft performed an emergency landing on Warsaw's runway 11, during which the nose gear folded from its unlocked position. The aircraft was evacuated, no injuries occurred. A technical narrative of the folding mechanism of the nose gear follows, which is not being understood with any degree of certainty needed for this summary.

On Jan 17th 2020 the PKBWL also released the English version of the interim statement. The report states that the drag strut assembly folded into the wrong direction evident by the Lower Drag Strut, the electrical harness and NGLK2 Proximity sensor face contacted each other. The report thus states: "The collision of the above elements was possible only if the strut was folded in the wrong direction (forward) - therefore the damage did not occur during the landing."

The lower lock link (LLL) was exposed to tearing forces, which caused it to fracture at its smallest sectional area (see photo below), when the upper drag strut and the lower drag strut were folding into the wrong direction. During a normal retraction the force would have been directed along the green arrow. The PKBWL wrote:

Damage (bending) of the LLL pin (Graphics/Photos below) indicates that the system was subjected to a great force while LLL movement was blocked, which occurs when LLL rests on the stop pin. Such conditions may occur when NLG is down and locked.

The LLL rests on the stop pin also when the NLG is completely retracted, but then the NLG system is not affected by any external force and in the investigated occurrence the NLG was not retracted.

The report states:

Analysis of the recorded data for SP-EQG showed that in addition to hard landings, there were also numerous cases of landings when the NLG sensor first responded, followed by the MLG sensor. The data from 1 January 2017 to the day of the accident were analyzed and they showed that there was 69 such cases (including one from the morning of the accident day),out of 2854 landings in the analyzed period. A common feature for the abovementioned 69 landings, apart from the order of the sensors loading, was a negative pitch angle.

The investigation asked the operator to check their FDR data for cases, in which the nose gear made ground contact prior to the main landing gear between Jan 1st 2017 and Jan 10th 2018. 398 landings on ten DH8Ds were identified meeting these criteria, of those there were 32 landings with pitch attitudes of more than 1.2 degrees nose down.

Related NOTAM:
A0261/18 - AD CLSD. 10 JAN 18:24 2018 UNTIL 10 JAN 22:30 2018 ESTIMATED. CREATED: 10 JAN 18:25 2018