Kabo B742 at Sokoto on Oct 4th 2013, touched localizer antenna on approach and burst body gear tyres
Last Update: November 27, 2020 / 00:37:38 GMT/Zulu time
Nigeria's Airport Authority reported the aircraft was cleared to land on runway 08 however the captain chose to land on runway 26 for undetermined reasons. The aircraft damaged the instrument landing system and came to a stop with deflated tyres.
The airline said, it was not an emergency landing, however confirmed the aircraft struck a sharp object and came to a stop with two body gear tyres deflated while landing in Sokoto to pick up more pilgrims. A replacement aircraft was to continue the flight to Jeddah.
Nigeria's AIB rated the occurrence a serious incident and opened an investigation dispatching investigators on site.
The replacement aircraft reached Jeddah on Oct 5th.
Sokoto offers a Cat I ILS approach for runway 08 and a VOR/DME approach for runway 26, runway length 3000 meters/9840 feet.
The weather station at Sokoto Airport [DNSO] transmitted only "NIL" METARs, there are no reports of a local weather station available as well.
On Nov 26th 2020 Nigeria's AIB (NAIB) released their final report concluding the probable cause of the serious incident was:
Inappropriate visual approach profile at night with no vertical guidance.
- Unserviceable Visual Approach Slope Indicator (VASI) on Runway 26.
- Decision to land on the non-precision runway 26 at night.
The NAIB summarized the sequence of events:
The Captain (52, ATPL, 13,805 hours total, 1,331 hours on type) was the Pilot Flying (PF) and the Co-pilot (27, CPL, 977 hours total, 649 hours on type) was the Pilot Monitoring (PM).
At 21:10 h, QNK617 contacted DNSO Air Traffic Control (ATC) and passed their traffic information. ATC acknowledged and cleared QNK617 as follows: QNK617 cleared Sokoto FL180, no delay. Expect ILS Approach Runway 08. Sokoto 20:00, Surface Wind calm, visibility 10km, Nil Weather, Few cumulonimbus North West at 750 m, QNH 1012.
At 21:12 h, Kano Control released QNK617 to Sokoto Control. At 21:24 h, QNK617 requested descent and was cleared to FL65 and instructed to report 25 DME SOK. At 41 DME SOK, QNK617 was re-cleared to 3500 ft on QNH 1012 and further cleared for ILS approach runway (RWY) 08 on reaching overhead SOK.
At 21:31 h, QNK617 reported field in sight and requested for straight-in Visual Approach for RWY 26. ATC replied as follows: no objection, report final runway 26. At 21:33 h, ATC cautioned QNK617 that the Approach Lights were of Low Intensity only and QNK617 acknowledged. At 21:36 h, QNK617 reported 8 miles final. ATC cleared QNK617 to land RWY 26 with reported surface wind calm.
During the landing approach, QNK617 impacted the Localizer Antenna/Approach Lighting System, touched down 100m short of RWY 26 threshold at 21:40 h and continued with the landing roll onto the runway until it came to a stop. The aircraft then taxied to the apron.
During the post incident interview, the crew stated that after shut down, they conducted a transit walk around and found two right main wheel tyres burst.
The Captain stated that the decision to land straight-in RWY 26 was to save fuel and that a 2.5 degree glide path was used for the approach. He also stated that the intention was to land at an appropriate point on the runway to avoid runway overrun, as the aircraft weight was close to maximum landing weight. He then added that he observed the absence of Touch Down Zone Lighting on the runway.
The Flight Engineer stated that the approach was normal until the Radio Altimeter call out of 10 ft, followed by a thudding sound and slight vibration.
After the post incident assessment, the crew disembarked the passengers. There was no injury to crew and passengers. The incident occurred at night in Visual Meteorological Condition (VMC).
The NAIB analysed:
Runway 08 had a serviceable ILS with low intensity Approach Lighting System (ALS) and an unserviceable VASI.
The Runway selected for use by the crew was RWY 26, it had no ILS but had VOR/DME (SOK) which was aligned with the runway. It also had a low intensity ALS and an unserviceable VASI.
Taking into consideration the risks inherent in a visual approach at night, even with the prevailing conditions of wind calm, ceiling and visibility okay, the appropriate choice of landing runway for this category of aircraft (category D) would have been the runway equipped with both vertical and lateral guidance (ILS), that was Runway 08.
The absence of guidance by the company for non-precision visual approach at night for this category of aircraft leaves the crew with the discretion of choice even when a precision approach facility like an ILS is available.
Approach and landing
Having elected to do a visual approach on runway 26, lateral guidance presents no issues as the VOR is aligned with the runway, ceiling and visibility were okay and the aircraft can be aligned visually. The VASI was unserviceable therefore there was no vertical guidance. SOK was serviceable to provide distance information to the runway.
During the approach briefing a continuous descent angle of 3 degrees should have been planned with distances to the threshold and the corresponding heights selected for distance/height cross checked so that the Pilot Monitoring can monitor and call out deviations.
Referring to B747–200 landing performance charts, using the same atmospheric conditions and information for the aircraft configuration at the time of the incident, the investigation determined the value of the required landing length limit obtained indicated that the runway is long enough for landing even at higher than maximum structural landing weight see Appendix II.
The captain reported that he wanted to land at the appropriate point because the aircraft is close to the maximum structural landing weight. This indicates probably that the briefing may not have considered the aircraft landing performance for that runway. The crew decided to conduct a visual approach and landing at night using a 2.5-degree continuous descent angle. Using the 2.5-degree glide path with distance/height crosschecks, the aircraft would have cleared the obstacles on the flight path. Therefore, the glide path flown must have been shallower resulting in the aircraft impacting the obstacles and touching down short of the runway.
This article is published under license from Avherald.com. © of text by Avherald.com.
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