Delta B763 at Madrid on Dec 5th 2013, burst tyre on takeoff, hydraulic failure, taxiway excursion after landing

Last Update: October 6, 2016 / 14:56:50 GMT/Zulu time

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Photo of Delta Airlines N182DN, Boeing 767-300 — Delta Airlines N182DN, Boeing 767-300 (Photo credit: Aero Icarus / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Dec 5, 2013

Classification
Accident

Cause
Hydraulic failure

Airline
Delta Airlines

Aircraft Registration
N182DN

Aircraft Type
Boeing 767-300

ICAO Type Designator
B763

Spain's CIAIAC released their final report concluding the probable causes of the accident were:

The incident was caused by the blowout of one of the main gear tires, caused by a metallic piece that had remained inside the tire during the retreading process.

The rubber that detached from the tire struck and perforated the underside of the right wing, damaging several hydraulic lines and rendering the airplane’s center and right hydraulic systems inoperative. A part from the hydraulic system then struck the top surface of the wing, perforating it as well.

The CIAIAC analysed that 15 minutes prior to the departure of DL-415 the departure runway had been inspected, the inspection team did not find any foreign objects or other anomalies on the runway. Following the departure and emergency declaration the same team inspected the runway again and easily found a metallic object as well as rubber debris on the runway. In trying to answer the question, whether the metallic object had been on the runway and penetrated the tyre of DL-415 or was embedded into the tyre the CIAIAC also analysed that if the object, rather thin and flat, had already been on the runway surface, the distance of the wheels in the wheel bogey made it unlikely the object could have been accelerated by the forward tyre sufficiently to penetrate the aft tyre. The CIAIAC therefore analysed: "After careful consideration of the two possibilities, this investigation concluded that the piece was inside the tire as the result of having been inserted there during the retreading process."

The CIAIAC analysed the actions of the crew: "The crew detected the problem because the airplane systems designed to notify them worked properly and they reported it immediately (24 s after the hydraulic system failure warning). They then took a reasonable amount of time to ascertain what was happening and decide if they had to declare an emergency. The conversations in the cockpit and between the crew and ATC clearly indicate that they resolved the situation ably, methodically and in keeping with procedures."

With respect to aircraft system design the CIAIAC analysed:

A fifth, and important, question that arises, this time involving the design of the aircraft, is if it is reasonable for a tire blowout to affect such critical systems on the airplane and why said systems are not better protected.

It must be noted that eight hydraulic system lines on the trailing edge were damaged, rendering the right and center systems inoperable, affecting the nose wheel steering system and the brakes, and leaving only the brake accumulator to stop the airplane. Also left inoperable were nine out of twelve air brakes and the right reverser. In addition to this, there was also significant structural damage, such as a fractured spar in the right wing.

The aircraft manufacturer shares this concern and is working to see how best to reinforce the protection for all the systems housed in the wings to avoid a reoccurrence of this event.

Understandably, the time period needed to draw satisfactory conclusions will be lengthy, but a safety recommendation is still being issued to the manufacturer to prevent a similar situation from happening in the future. Although these actions are already underway and both the FAA and EASA are reviewing the certification rules, meaning the results of all this work must be known before a determination can be made on improving the safety and protection of these and other systems located in the wing, issuing a recommendation offers a suitable means of tracking all this work.

Finally, there is a sixth and final question stemming from this event, namely, why the aircraft did not stop on the runway if the distance specified in the QRH was below that available for landing and the airplane touched down very close to the threshold.

Boeing’s QRH has a section with tables for calculating landing distances. These tables are calculated to include the distance from the time the airplane is at an altitude of 1,000 ft until it is over the runway threshold plus the actual distances on the ground.

Taking into account the loss of the center and right hydraulic systems, and for the weight, pressure altitude, temperature and runway conditions present, the landing distance should be about 7,500 ft. This figure does not include the effect of a blowout, which is not considered among those configurations for which a landing distance in published.

The difference between the figures in the table and the actual distance traveled is that the braking distance expressed in the QRH is not calculated using a specific braking model that uses all the liquid in the accumulator; instead, it is calculated using a model that assumes that the hydraulic system is fully active for braking and the efficiency of the accumulators is overestimated in comparison to that of the system as a whole.

This is obviously not the correct way to do the calculation, as it does not take into account the finite nature of the accumulator as a source of pressure. In reality, the pressure on the brakes is supplied by the accumulators as the fluid in them, fluid that cannot be replenished, is exhausted.

To address this, the manufacturer is working to ensure that the QRH considers every case, including the scenario specific to this event. However, due to the importance of having this information available as soon as possible, a safety recommendation is being issued to the manufacturer to make the necessary changes to the QRH such that it reflect the actual landing distance required.

It would also be appropriate for the manufacturer to inform other operators using similar airplanes in their fleets of any progress made in these areas.