Iberia MD88 at Vienna on Jul 31st 2008, burst tyre, engine failure, gear unsafe indication

Last Update: October 20, 2013 / 20:09:51 GMT/Zulu time

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Incident Facts

Date of incident
Jul 31, 2008

Classification
Accident

Cause
Engine failure

Airline
Iberia

Aircraft Type
McDonnell Douglas MD-88

ICAO Type Designator
MD88

On Oct 17th 2013, more than 5 years after the occurrence, Austria's Accident Investigation Unit ("Verkehrssicherheitsarbeit für Österreich", VERSA) released their final report in German but retracted the report on Oct 18th 2013 stating: "Der Untersuchungsbericht MD 88 vom 31.07.2008 wurde aus ermittlungstechnischen Gründen entfernt. Bereits ausgedruckte oder gespeicherte Versionen dieses Berichtes sind mit sofortiger Wirksamkeit ungültig." (Translation: The investigation report MD-88 of July 31st 2008 was removed for investigation technics reasons. All already printed or stored versions of this report are invalid with immediate effect).

Observing this statement and cautioning readers about that legal status of the report The Aviation Herald publishes this invalid Final Report in German nonetheless as it appears to provide insight into the sequence of events.

This invalid final report concluded the probable causes of the serious incident were:

- disruption of electric components of the proximity switch in the left main gear well by foreign objects
- intrusion of foreign objects into the left hand engine

Probable factors:

- unsecured attachment of the tyre valve in rim #2
- it is unclear what additional maintenance works were conducted in the area of the tyre valve by the operator while the tyre was replaced
- use of a porous O-ring in the valve on rim #2
- insufficient grease of the O-ring
- on the day of the incident a loss of pressure in the tyre was not detected, it is to be assumed that the pressure had not been measured
- indications of a separation of the tread from tyre #2 were not detected during pre flight checks

Possible factors

- insufficient torque moment during attachment of the valve during the tyre replacement on Jul 11th 2008

The captain (58, ATPL, 15,818 hours total) and first officer (38, ATPL, 5,246 hours total) formed the crew, the report did not establish who was pilot flying and who pilot monitoring.

VERSA reported that the aircraft departured Vienna's runway 29, while becoming airborne the left hand engine (JT8D) lost power and started to vibrate. The crew retracted the landing gear, declared Mayday and positioned for an approach to runway 29 for an immediate return. While on downwind at 2000 feet MSL the crew detected smell of smoke in the cockpit, there was no fire indication however and no smoke was observed. The crew worked the checklists for "engine fire or severe damage or separation" and emergency return to the airfield, the left hand engine was shut down. The APU was started, the hydraulic pump and electric generator of the APU were connected. After the gear was extended the left hand main gear did not indicate down and locked, the crew therefore flew a 360 and worked the checklist abnormal gear indication with handle down and activated the alternate gear extension, the left main gear however continued to indicate unsafe. The crew decided to abandon the approach and subsequently performed a low approach along runway 29 in about 500 feet AGL to have the gear inspected from the tower. Tower reported the gear was down, the crew subsequently climbed the aircraft to 5000 feet MSL.

In the meantime a runway inspection found parts of a tyre and a part of a chine. The first officer attempted to inspect the gear through a periscope in the passenger cabin however were unable to see the gear due to dirt obscuring the periscope.

21 minutes after departure the crew conducted another overflight along (but not above) runway 29 at 400 feet AGL which again resulted in the information that the left main gear was down. The aircraft climbed again to 5000 feet and entered a hold to burn off fuel and prepare a landing with unsafe gear and a possible evacuation.

After sufficient fuel had been burned off to bring the aircraft to below the maximum landing weight the crew performed a landing on runway 34, which is longer and offers wider safety areas to the left of the runway, the crew requested the runway to be foamed for the possibility of a gear collapse - which according to strategies and ineffectiveness of the procedure was not complied with.

The aircraft landed safely on runway 34 76 minutes after departure, the open gear doors as result of the alternative gear extension contacted the runway surface however and caused sparks. The aircraft rolled out safely and vacated the runway via exit 32, the passengers disembarked onto the taxiway.

The aircraft received substantial damage to the left main gear, left flaps, both inner gear doors and the left main gear well. The inboard left hand tyre was flat with the tread separated.

VERSA reported the outboard left tyre showed a pressure of 192 PSI with a normal pressure of 200 PSI and the lower limit of 190 PSI.

VERSA reported that the defective tyre #2 had been produced on May 13th 2007 and had flown 225 cycles on another aircraft before it needed to be replaced due to a cut in the tread. The tyre was sent to the manufacturer for repair and was returned repaired on March 11th 2008. On July 11th 2008 it was then mounted on rim #2 in a licensed maintenance facility, a subsequent 24 hour test for tightness proved the tyre was tight and holding pressure, the tyre was not moved or put under load during that test. The tyre pressure was reduced to storage pressure of 40 psi afterwards.

The rim and tyre was mounted on the incident aircraft on Jul 30th 2008, the storage pressure of 40 psi was increased to 200 psi. The aircraft performed five sectors on Jul 30th 2008.

In the night from Jul 30th 2008 to Jul 31st 2008 a tyre pressure of 200 psi was confirmed by signature on all 4 tyres.

Following the incident flight the defective tyre was taken the tyre manufacturer for tests, no penetrations were found and tests conducted with intact valves confirmed the defective tyre was tight and held pressure. All marks on the tyre including the fractures causing the separation of the tread are consistent with the tyre losing pressure completely, according to experience one takeoff with such a pressure loss is sufficient to cause the damage as observed on the incident tyre.

When the tyre was mounted on the rim there was no requirement to dismount the valve or check its function. However, there are indications that the valve was dismounted. It was found that the thread of the valve connecting the valve to the rim was not secured, which was not required nor designed. The valve was found to be torqued to a point where a human being could unscrew it without tools. The O-ring under the valve was found damaged and porous. Further examination showed that the valve itsself was tight, the O-ring however had only little traces of grease on one side, was porous and had accumulated what is believed to be particles of abrasions of brakes.

VERSA analysed that during the mounting of the incident tyre on rim #2 on Jul 11th 2008 the valve was dismounted, when the valve was reinstalled the O-ring was not replaced and was not greased as required. When the valve was torqued the O-ring was most likely damaged or already fractured. Due to lack of movement and load the problem was not discovered during the leak test. After the wheel was mounted on the incident aircraft on Jul 30th 2008 the loads and movements, aggravated by the failure of auto brakes, led to a loss of tyre pressure. That loss however was not discovered during the maintenance check in the night to Jul 31st 2008, the beginning separation of the tread was not noticed during preflight checks for the incident flight.

VERSA analysed that the overflight along the runway introduced the risk of unknown terrain, especially on single engine the safety margins could have been compromised during climb out and were left to "random factors". VERSA argued that a low approach following published approach and go-around procedures would have eliminated that risk and appeared more prudent. In particular, the situation at Vienna required overflying an oil refinery and chemistry factory, the failure of the other engine at that point could have resulted in excessive consequences.
Incident Facts

Date of incident
Jul 31, 2008

Classification
Accident

Cause
Engine failure

Airline
Iberia

Aircraft Type
McDonnell Douglas MD-88

ICAO Type Designator
MD88

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