Pen SB20 at Unalaska on Oct 17th 2019, overran runway on landing

Last Update: November 18, 2021 / 20:52:22 GMT/Zulu time

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Incident Facts

Date of incident
Oct 17, 2019

Classification
Accident

Airline
Penair

Flight number
AS-3296

Aircraft Registration
N686PA

Aircraft Type
SAAB 2000

ICAO Type Designator
SB20

Airport ICAO Code
PADU

A PenAir Saab 2000 on behalf of Alaska Airlines, registration N686PA performing flight AS-3296 from Anchorage,AK to Unalaska,AK (USA) with 38 passengers and 3 crew, overran the end of the runway while landing on Unalaska's Dutch Harbour Runway 13 at 17:34L (01:34Z). The aircraft came to a stop about 125 meters/400 feet past the end of the runway partially hanging down a slope into the sea, the left hand propeller blades had contacted some obstacles, blades impacted and penetrated the fuselage. One passenger died as result of the accident, one passengers received serious injuries, three received minor injuries. One injured passenger was flown out to Anchorage. A total of eleven passengers were taken to a hospital.

There is a mismatch between pictures from Unalaska showing N686PA involved in the accident, while Mode-S data identify N681PA as the aircraft performing the flight to Unalaska while N686PA landed in Anchorage at the same time as flight AS-3295 from Unalaska. The FAA aircraft registration data support that identification by Mode-S data, that N686PA was the aircraft landing in Anchorage at that time.

The NTSB have opened an investigation. Nine investigators were dispatched to Unalaska.

Local Authorities reported all members of a youth swim team on board of the aircraft remained unhurt. Three passengers were taken to a hospital sitting upright and conscious, a number of other passengers were checked at the airport.

The FAA reported there were 38 passengers and 3 crew on board. The airline reported 39 passengers and 3 crew on board.

A ground observer reported the aircraft had attempted landing on runway 13, overflying Hog Island first flying with the wind, but went around, positioned for another approach to runway 13 again with the wind, touched down but did not stop, there was deceleration however.

A Medevac aircraft departed Cold Bay,AK (USA) about 90 minutes after the occurrence and landed in Unalaska about 2:20 hours after the occurrence. The Medevac Aircraft departed for Anchorage after about 90 minutes on the ground. The aircraft carried one of the injured passengers to Anchorage for further treatment.

On Oct 18th 2019 Alaska's Department of Public Safety reported that one passenger died due to traumatic injuries, another one was medevaced to Anchorage. The Fire Department transported 7 passengers to the local hospital, 4 more passengers arrived in the hospital by private vehicles.

On Oct 21st 2019 Sweden's Haverikommission (SHK) reported they have assigned an accredited representative to join the investigation by the NTSB. According to the NTSB one passenger was killed, two passenges received serious and five passengers received minor injuries when the aircraft overran the runway and stopped with the nose down almost in a nearby river.

On Nov 15th 2019 the NTSB reported one passenger was fatally injured, 1 passenger received serious and three minor injuries when it overran the runway, broke through the airport perimeter fence and came to rest on shoreline rocks. The NTSB is investigating the accident.

In a separateöy released investigation update the NTSB reported the captain (ATPL, 20,000 hours total, 101 hours on type) was pilot flying, the first officer (ATPL, 1,446 hours total, 147 hours on type) was pilot monitoring. The crew reported they had gone around on the first approach because of not being stabilized. On the second approach they touched down 1000 feet down the runway, the captain applied normal reverse thrust and wheel braking. At the 80 knots call the captain went to maximum braking. When the aircraft went beyond the runway end they attempted to steer the aircraft to the right to avoid going into the water.

The NTSB reported there were rubber witness marks, 5 inch wide, on the runway about 15 feet left of the runway center line starting 1840 feet past the displaced threshold of the runway 13 and extended about 200 feet. Small fragments of a tyre were found in the area near the witness mark. The left outboard main tyre was found deflated with an area that had worn entirely through the tyre. Tyre witness marks of all tyres but the outboard left main were found in the runway overrun area in an arc to the right.

The NTSB wrote: "The left wing or left engine propeller struck a 4 to 5 ft vertical signal post on the opposite shoulder of the road and the left propeller struck a 6 to 8-ft high yellow diamond shaped road sign. There were strike marks consistent with the right engine’s propeller tips contacting the ground near where the airplane came to rest. ... A propeller blade was loosely stuck in the surrounding structure external to the fuselage and another propeller blade was found inside the fuselage."

The NTSB reported according to the FDR the aircraft touched down at 129 KIAS and 142 knots over ground. Following touchdown the aircraft reached a maximum deceleration of -0.48G with the engines operating in reverse mode. About 25 seconds after main gear touch down "a change in aircraft pitch and roll, and an increase in the magnitude of triaxial acceleration forces was recorded, consistent with the aircraft departing the runway surface. The engines were taken out of reverse mode and ground speed at that time was about 23 knots."

The NTSB reported based on the CVR that for the first approach the winds had been reported from 180 degrees at 7 knots, after the go around the winds were reported from 290 degrees at 16 knots gusting 30 knots, however, multiple transmission overlaid at that time. During the second approach winds were then reported from 300 degrees at 24 knots.

On Dec 17th 2020 the NTSB released a very brief preliminary report and opened their public docket.

The most notable new information contained in the docket concern the aircraft's anti skid system on the left main gear. The FDR group's factual report reports anti-skid faults during roll out:

Accelerations consistent with main gear touchdown occurred at 1739:54 AKDT, followed by the nose gear at 1739:55 AKDT, and the 1 Hz Gear Weight on Wheels signal became true at 1739:56. Indicated airspeed at main gear touchdown was about 125 kts and ground speed was about 141 kts. Rate of deceleration increased over the three seconds following main gear touchdown to a peak of -0.48 g. During this time, the flaps retracted by 5 degrees and both propellers transitioned to beta mode with the engines controlling to ground idle propeller speed (Np).

At 1739:59 AKDT, longitudinal deceleration changed from a smooth deceleration to a slightly oscillatory profile, with variations of approximately 0.03 g at each 0.25 second sample of longitudinal acceleration and an overall trend toward less deceleration. Also during this time, an Anti-Skid Inboard Fault Caution became active. This oscillatory and decreasing deceleration behavior continued for the next 11.5 seconds, when the longitudinal acceleration had reached -0.17 g and ground speed was 54 kts. The decreased deceleration behavior was despite the engines transitioning from ground idle beta to max reverse power at 1740:03 AKDT.

At 1740:10 AKDT, the longitudinal deceleration profile became smooth for 5.5 seconds and the Anti-Skid Inboard Fault Caution transitioned to inactive. Engine power lever angles (PLAs) stayed at about 1 degree, consistent with commanding maximum reverse power, and deceleration rate remained steady between -0.16 g and -0.2 g. At 1740:16 AKDT, the oscillations in longitudinal acceleration resumed and the Anti-Skid Inboard Fault Caution reactivated with ground speed at 34 kts.

Two seconds later, at 1740:18 AKDT, the engine PLA began to increase from about 1 degree to about 35 degrees, consistent with idle power, over 3 seconds. The engines and propellers transitioned to idle power and beta mode, respectively. At 1740:19 AKDT, changes in pitch, roll, and vertical and longitudinal accelerations were consistent with a departure of the runway surface. Ground speed at this time was 23 kts.

One second after runway departure, the weight on wheels and left main gear down and locked signals became false, consistent with damage to the left main gear. About one second after that the left engine gas generator speed dropped to 0%, consistent with damage to the left engine.

The recording stopped at 1740:31 AKDT and the data is consistent with a sudden power interruption to the recorder. The final three seconds of recorded data are unreliable, as evidenced by invalid data during this time including the aircraft attitude and ground speed.

The System and Structures factual report states after matching cables, that were fractured as result of the impact forces:

The short segment was also able to be matched with the recovered MS 27467T9B35P connector, which could only have been attached to the 5GA-J4 bulkhead fitting. According to the installation instructions detailed above, this harness should have been routed to the #2 wheel, not the #1 wheel. This showed the left gear wheel speed transducer wire harnesses were incorrectly installed. The examination showed that the right gear wire harnesses were installed correctly.

Following a board meeting on Nov 2nd 2021 the NTSB released following abstract of the board meeting stating the probable causes of the accident were:

Probable Cause

We determined that the probable cause of this accident was the landing gear manufacturer’s incorrect wiring of the wheel speed transducer harnesses on the left MLG during overhaul. The incorrect wiring caused the antiskid system not to function as intended, resulting in the failure of the left outboard tire and a significant loss of the airplane’s braking ability, which led to the runway overrun. Contributing to the accident were (1) Saab’s design of the wheel speed transducer wire harnesses, which did not consider and protect against human error during maintenance; (2) the FAA’s lack of consideration of the RSA dimensions at DUT during the authorization process that allowed the Saab 2000 to operate at the airport; and (3) the flight crewmembers’ inappropriate decision, due to their plan continuation bias, to land on a runway with a reported tailwind that exceeded the airplane manufacturer’s limit. The safety margin was further reduced because of PenAir’s failure to correctly apply its company-designated PIC airport qualification policy, which allowed the accident captain to operate at one of the most challenging airports in PenAir’s route system with limited experience at the airport and in the Saab 2000.

On Nov 18th 2021 the NTSB released their final report.

Related NOTAMs:
!DUT 10/064 DUT RWY 13 RWY END ID LGT U/S 1910180706-1910232000EST
!DUT 10/063 DUT RWY 13 VASI U/S 1910180702-1910232000EST
!DUT 10/060 DUT AD AP CLSD 1910180209-1910190209
!DUT 10/062 DUT RWY 13/31 NW 4000FT CLSD EXC MEDEVAC 1910180307-1910190307
!DUT 10/061 DUT RWY 13/31 SE 500FT CLSD 1910180254-1910190254

Metars:
PADU 180356Z VRB04KT 10SM BKN032 BKN042 07/01 A2953 RMK AO2 SLP003 T00670006=
PADU 180256Z 25004KT 10SM BKN035 BKN044 BKN120 07/02 A2952 RMK AO2 RAE14 SLP002 ACSL NE P0002 60004 T00670017 53003=
PADU 180156Z 30021G27KT 5SM -RA BKN039 06/02 A2953 RMK AO2 PK WND 30027/0154 RAB41 SLP004 P0002 T00560017=
PADU 180056Z 31011KT 10SM FEW034 BKN047 BKN060 07/01 A2950 RMK AO2 SLP995 T00720011=
PADU 172356Z 31006KT 10SM BKN036 BKN044 07/01 A2951 RMK AO2 RAB12E25 SLP999 P0000 60000 T00670011 10083 20056 53005=
PADU 172256Z 19008KT 10SM BKN037 BKN047 07/01 A2950 RMK AO2 WSHFT 2210 RAB07E18 SLP994 P0000 T00720011=
PADU 172230Z 28008KT 10SM FEW033 BKN060 07/01 A2950 RMK AO2 WSHFT 2210 RAB07E18 P0000=
PADU 172156Z 25008G22KT 10SM BKN055 08/M01 A2950 RMK AO2 SLP993 T00831006=
PADU 172056Z 29010KT 10SM FEW025 BKN034 BKN049 06/02 A2950 RMK AO2 PK WND 29028/2035 RAB34E51 SLP994 P0000 60000 T00610017 53007=
Incident Facts

Date of incident
Oct 17, 2019

Classification
Accident

Airline
Penair

Flight number
AS-3296

Aircraft Registration
N686PA

Aircraft Type
SAAB 2000

ICAO Type Designator
SB20

Airport ICAO Code
PADU

This article is published under license from Avherald.com. © of text by Avherald.com.
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