Sudan MD83 at Juba on Jun 23rd 2006, runway excursion

Last Update: May 22, 2013 / 23:03:54 GMT/Zulu time

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Incident Facts

Date of incident
Jun 23, 2006

Classification
Report

Flight number
SD-325

Destination
Juba, Sudan

Aircraft Registration
SU-BOZ

ICAO Type Designator
MD83

A Sudan Airways McDonnell Douglas MD-83, registration SU-BOZ performing flight SD-325 from Nairobi (Kenya) to Juba (Sudan) with 12 passengers and 12 crew, positioned for an approach and landing on Juba's runway 31 in visibility of 10km, winds from 180 degrees at 3 knots and temperature 31 degrees C, no clouds were reported (editorial note: but also no CAVOK). The captain (52, ATPL, 7,673 hours total, 2,179 hours on type) was pilot flying, the first officer (43, no license type provided, 433 hours total, 260 hours on type) was pilot monitoring, a second captain (42, 8,497 hours total, 1,135 hours on type) was on the observer's seat. The crew configured the aircraft for landing with flaps 40. The aircraft touched down on runway 31 (length 2400 meters/7870 feet) 698 meters past the threshold at a speed of 130 knots, spoilers deployed automatically, thrust reversers were engaged, the left hand spoilers however retracted again with the right hand spoilers (editorial note: FDR recording has left/right crossed) remaining deployed. The aircraft slowed to 80 knots, the thrust reversers were stowed, the captain then felt lateral instability and shaking of the aircraft and asked the first officer whether he was operating the rudder. After the first officer replied in the negative, the captain decided to use manual braking and pressed the brakes pedals, however had the impression the brakes were not working. The aircraft slowed to 60 knots and was approaching the runway end, so that the captain decided to engage reverse thrust again and deployed the thrust reversers a second time. The aircraft veered to the right and accelerated, went off the runway and came to a stop about 300 meters off the paved extension of runway 31 with the nose gear and left main gear collapsed. The aircraft was evacuated, no injuries occurred. Tower instructed the crew to backtrack the aircraft to the apron.

The aircraft received substantial damage, two runway end lights were damaged.

Sudan's Central Directorate of Air Accident Investigation (SAAICD) released their final report concluding the probable cause of the serious incident (editorial note: the AVH thinks classification as accident is more appropriate considering the structural failure of the landing gear) was:

Late touch down point down sloped R/W 31, reduced brake effect and imposed lateral acceleration that puzzled the PIC and attracted his attention to counteract the unexpected phenomena is the main reason to this serious incident.

- Poor maintenance and improper before flight and landing checks are considered to be a contributory factor to this serious incident.

The SAAICD reported that the aircraft was leased in from AMC Airlines (Egypt), but was operated by Sudan Airways. All flight crew were citizens of Egypt.

The SAAICD analysed that the recordings for left and right hand systems were swapped on the flight data recorder, that was successfully read out along with the cockpit voice recorder, both recorders containing the occurrence flight recordings.

The FDR revealed that the left hand hydraulic system was inoperative at the time of the landing, brakes pressure was supplied only from the right hand hydraulic system. The automatic brakes engaged, brakes pressure built up but was released without disarming the autobrakes according to system design when the left hand spoilers retracted. The captain felt deceleration was insufficient and switched to manual braking, the brakes pressure built up reaching a maximum of 670 psi. The aircraft slowed down to 48 knots, by then the brakes pressure was "exhausted" and had dropped to 311 psi.

The SAAICD stated: "Inefficient braking, dropping and rising of brake pressure might be due to a defect within the power transfer unit or the unit being closed due to leakage of hydraulic fluid from the left system. At that moment the right Hydraulic System was exhausted and the aircraft was rolling down slope of R/W 31, the speed started to increase due to its inertia force and passed the paved extension of runway 31 with speed of 58 Kts., and rolled into the soft ground with increasing speed of 69 knots and warning horn sound indicating landing gear up at a distance of 129 meters ( 423 feet ) from the end of paved extension of R/W 31."

The SAAICD analysed, that due to the failure of the left hand hydraulics system the left hand thrust reverser deployed to its extended position during the first application of reverse thrust using the hydraulics accumulator, which was exhausted after engaging the thrust reverser. During the subsequent stowing of the reversers the left hand reverser likely did not completely stow. When the thrust reversers were deployed a second time, the right hand thrust reverser was brought into its fully deployed position by the right hand hydraulics, the left reverser however remained in its near stowed position, the left hand engine thus developed forward thrust accelerating the aircraft and causing it to veer to the right.

The SAAICD analysed that no traces of hydraulic fluid were found along the path of the aircraft on the runway to the final position. It was thus "probable that the system defused amount of fluid during flight which was unnoticeable by the crew. Spillage of hydraulic fluid during flight might be due to the imposed vibration acquired by the hydraulic pipe of P/N 7936907-711 due to breakage of the clip securing the pipe to the undercarriage bay due increased strain that occurred due to loose tightening. The vibration of the pipe lead to movement of the pipe flattened end at the connection with the reservoir thus disseminating fluid to atmosphere."

The SAAICD analysed that tower obviously could not see the runway and did not recognize the aircraft had gone off the runway.
Incident Facts

Date of incident
Jun 23, 2006

Classification
Report

Flight number
SD-325

Destination
Juba, Sudan

Aircraft Registration
SU-BOZ

ICAO Type Designator
MD83

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