Daily DHC6 at Kaohsiung on Apr 23rd 2018, runway excursion on landing
Last Update: April 19, 2019 / 16:33:47 GMT/Zulu time
Date of incident
Apr 23, 2018
De Havilland DHC-6 Twin Otter
ICAO Type Designator
Airport ICAO Code
On Apr 25th 2018 Taiwan's ASC reported the aircraft veered off runway 09 at 17:22L. Cockpit voice and flight data recorders were retrieved, the investigation team has completed the aircraft system test, flight crew interviews, site survey and airport facilities survey. The investigation into the occurrence is ongoing.
On Apr 19th 2019 Taiwan's ASC released their executive summary of the final report concluding the probable causes of the incident were:
Finding related to probable causes
- The occurrence aircraft landed in a right crosswind. After touchdown, the pilot flying (PF) attempted to correct the lateral deviation but misused the nose wheel steering lever which caused the aircraft veered-off the runway from its left hand side with a 35 degrees drift angle. The aircraft turned 180 degrees left and stopped on the grass area.
Findings related to risk
- At the time of the occurrence, the DHC-6-400 level D flight simulator was not yet available in the aviation industry. The Daily Air could only carry out pilot training and check in a real aircraft. However, it is not only impossible to simulate various scenarios and weather conditions in a real aircraft, but also contained higher risks, thus restricted the effectiveness of pilot training and check.
- Daily Air did not specify standard call-outs in relevant manuals for pilot monitoring (PM) to remind lateral deviation during landing roll. Thus the flight crew acted on their own style and it weakened the effectiveness and accuracy of the communication.
- Daily Air did not specify the timing or speed limit in relevant manuals for the use of "nose wheel steering". It may result in divergence of views and actions toward this issue and adverse effect on standardization in the DHC-6-400 fleet.
- Daily Air did not have a clear policy regarding the usage of asymmetric thrust to assist directional control during landing roll. There were divergences in opinions between management, instructor pilots, check airmen and flight crew in the DHC-6-400 fleet.
- The captain of this occurrence had already carried out all flying tasks, including take-off and landing operations manually for 8 legs, and his flight duty period had exceeded 10 hours. The captain’s decayed physical and mental conditions due to his accumulated workload could weaken his alertness and ability to perform tasks safely.
- Although flight crew schedules of Daily Air was in compliance with the CAA regulations, a bio-mathematical model analysis of pilot fatigue showed that the eastern Taiwan routes with 12 legs a day may exist a high risk of fatigue, the Taiwan eastern routes with 10 legs a day may exist a moderate-to-high risk of fatigue; the western Taiwan routes with 8 legs a day may exist a moderate risk of fatigue.
- Shortage of pilots in Daily Air DHC-6-400 fleet has existed at least for a year before the occurrence happened, especially in the case of a shortage of captains, which may result in high risk of fatigue on the pilot flight schedule.
- The cockpit of DHC-6-400 aircraft owned by Daily Air was not equipped with effective air-conditioning, which may result in unpleasant mental situation or fatigue of flight crew members due to potentially heat stress environment.
- Daily Air failed to completely integrate its internal evaluation programs of its flight operations division in the safety management manual. The internal evaluation program was scattered over its flight operations manual and the safety management manual, which is harmful to the implementation and review of internal evaluation programs.
- According to the safety management manual of Daily Air, flight crew recurrent flight check was included in the internal evaluation programs. However, the flight check is an essential requirement to maintain pilot qualification, which should not be classified as internal evaluation programs.
- The flight crew were certificated and qualified in accordance with the Civil Aeronautics Administration regulations and company requirements. No evidence indicated any preexisting medical conditions or alcohol that might have adversely affected the flight crews’ performance during the occurrence flight.
- The pilot flying completed the transition as well as upgrade training and check on DHC-6-400 type one month before the occurrence. He has accumulated 204 hours and 8 minutes on DHC-6-400. No anomaly related to this occurrence, such as "direction control during landing roll" or "usage of nose wheel steering" was found in his training records.
- At the time of the occurrence, surface winds of runway 09 in Kaohsiung airport were blowing from the right with the velocity of 10 knots to 19 knots. The weather condition was within the limits of DHC-6-400 fleet.
- All available evidences indicated that the nose wheel of the occurrence aircraft should be in the center position before landing. The possibility of veered-off due to nose wheel steering malfunction was ruled out.
- The nose steering system and hydraulic system were normal during the landing roll period.
- The output torque difference between two engines was about 1%, and gas generator speed of the left engine (Ng) was 1% lower than the criteria at the idle from the maintenance manual during performing post-occurrence engine examination, were not considered as influences in aircraft controlling or might have resulted in a significantly directional change.
The ASC described the sequence of events stating the captain was pilot flying:
The occurrence aircraft maintained 4,000 feet for cruising and flew southeast bound after take-off, the flight joined SIGANG ONE KILO ARR (SN1K), then the crew made a visual approach to runway 09 of Kaohsiung Int. airport (RCKH) which was cleared by Kaohsiung approach at 1715. The Kaohsiung Control instructed runway 09 in use, wind condition 180/12 knots, and cleared the flight to land.
The landing reference speed (VREF) of the occurrence aircraft was 75 knots, flap 20 degrees, and the approach speed (VAPP) was 80 knots. At 1720 the flight crew performed final checklist, the item of “nose wheel steering” was read out by PM, PF replied “centered and locked”. When the aircraft descended through 200 feet agl, the PM called out “right 17 (crosswind) tail 2 (tailwind)” to inform the captain wind condition from the navigation display (ND).
According to flight data recorder data and results of site-survey, the occurrence aircraft landed at 1,360 feet from runway 09 threshold at 1722:10. The tire marks were found in front of the aiming point, with right landing gear touched ground first before the right-wing tilted up slightly. The tire marks were left starting from 1,675 feet from the threshold, 5 feet to the right-side of runway centerline. The tire marks started to drift to right about 5 degrees w.r.t. the centerline while the occurrence aircraft passed through taxiway Bravo during deceleration, but it drifted to left when it reached around 2,100 feet from the threshold afterwards.
The occurrence aircraft veered off from the left-hand side of runway 09 with 35 degrees drift angle, and crossed the runway edge at approximately 2,500 feet from the runway threshold, and finally it stopped on the grass area at 2,630 feet from the runway threshold, 180 feet away from the runway edge, the heading toward 276 degrees, which was opposite to its landing direction. There was no injury and the right landing gear was deflated due to tire departed from the barrel.
RCKH 231030Z 17011KT 140V210 9999 FEW013 BKN220 29/25 Q1008 NOSIG RMK A2978=
RCKH 231000Z 16012KT 130V210 9999 FEW015 BKN250 29/24 Q1008 NOSIG RMK A2977=
COR RCKH 230942Z 18011KT 140V210 9999 FEW015 BKN220 29/25 Q1008 NOSIG RMK LOCAL REPORT A2977=
RCKH 230930Z 18012KT 150V230 9999 FEW015 BKN220 29/24 Q1008 NOSIG RMK A2977=
RCKH 230900Z 18013KT 150V220 9999 FEW016 BKN220 29/24 Q1007 NOSIG RMK A2976=
RCKH 230830Z 18014KT 160V220 9999 FEW018 SCT220 29/24 Q1007 NOSIG RMK A2975=
RCKH 230800Z 19016KT 9999 FEW018 30/24 Q1007 NOSIG RMK A2976=
RCKH 230730Z 19015KT 150V220 CAVOK 30/24 Q1007 NOSIG RMK A2975=
RCKH 230700Z 19013KT 150V230 CAVOK 31/23 Q1007 NOSIG RMK A2975=
RCKH 230630Z 19014KT 150V220 9999 FEW016 31/23 Q1008 NOSIG RMK A2977=
Date of incident
Apr 23, 2018
De Havilland DHC-6 Twin Otter
ICAO Type Designator
Airport ICAO Code
This article is published under license from Avherald.com. © of text by Avherald.com.
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