Avianca F100 at Brasilia on Mar 28th 2014, landed without nose gear

Last Update: July 17, 2020 / 17:31:52 GMT/Zulu time

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Incident Facts

Date of incident
Mar 28, 2014

Classification
Accident

Airline
Avianca Brasil

Flight number
O6-6393

Departure
Petrolina, Brazil

Destination
Brasilia, Brazil

Aircraft Registration
PR-OAF

Aircraft Type
Fokker 100

ICAO Type Designator
F100

An Avianca Brasil Fokker 100, registration PR-OAF performing flight O6-6393 from Petrolina,PE to Brasilia,DF (Brazil) with 44 passengers and 5 crew, was on approach to Brasilia when the crew reported an unsafe gear, aborted the approach and entered a hold to work the related checklists, but were unable to resolve the problem. The crew declared emergency and prepared for a possible partial gear landing at 17:42L (20:42Z) about 60 minutes after aborting the first approach. The aircraft landed on Brasilia's runway 11R on its main gear, the crew held the nose up as long as practicable before lowering the nose onto the runway and coming to a stop on the runway. Emergency services foamed the aircraft. There were no injuries, the aircraft sustained substantial damage.

The runway was closed.

Brazil's Department of Civil Aviation reported the aircraft had suffered a hydraulic failure leading to the nose gear failure.

On Aug 19th 2014 the Dutch Onderzoeksraad (DSB) reported in their quarterly bulletin that the nose gear could not be extended during the approach, the emergency extension also did not work. The crew thus performed a landing with the nose gear remaining retracted. There were no injuries, the aircraft sustained substantial damage. The DSB is providing assistance to the investigation led by Brazil's CENIPA.

On May 29th 2020 Brazil's CENIPA released their final report concluding the probable causes of the accident were:

Aircraft maintenance – undetermined.

It was found that there was a restriction on the articulation movement of the right nose landing gear door and that the weight of this landing gear was not sufficient to overcome such restriction.

Upon inspecting the hinges, it was found that there were no signs of recent lubrication, allowing the hypothesis of occurrence of any deviation or non-adherence to the inspection and lubrication requirements established by the manufacturer leading to a the scenario favorable to the right door movement restriction.

The issue of the maintenance could also be related to some deviation, or nonadherence to the requirements established for the service of widening the holes of the hinges concerning the coating and corrosion protection of the worked surface. As a result, the area could have been more susceptible to corrosive processes.

Project – undetermined.

The maintenance program, established by the manufacturer, may have contributed to the occurrence by not establishing adequate preventive maintenance parameters for the landing gear doors that were modified by reworking the hinges, incorporating larger radial pins and widening the lobe holes.

Other – undetermined.

It was not possible to determine the causal root of the EDP1 gasket extrusion, which caused the leakage of hydraulic oil that caused the hydraulic system 1 to fail.

CENIPA analysed:

All procedures adopted by the crew regarding the management of the fault presented by the hydraulic system 1 occurred in accordance with the provisions of the aircraft operation manuals.

Through the examinations and tests conducted on the aircraft, as well as its components, it was found that the lowering and locking of the nose landing gear through the alternate system would not be possible, due to technical problems, which will be explained throughout the present analysis.

During the investigation, it was found that there was fluid leakage through the body of one of the hydraulic pumps, called EDP 1, which was installed on the left engine of the aircraft. Considering that there was no previous report of the malfunction of the hydraulic system and that the aircraft preparation procedures were carried out satisfactorily before the Petrolina takeoff, it can be stated that the leak, at least with regard to large proportions of hydraulic fluid, occurred from the takeoff of that locality.

The leak was such that it caused the collapse of the hydraulic system 1 about thirty minutes after takeoff.

Research conducted on the hydraulic pump was sufficient to identify that fluid leakage occurred due to extrusion of a molded gasket. This gasket was between two sections of the pump body in an area that was only worked on when the pump was submitted to repairs or overhaul.

The pump in question had been repaired and tested on 31JUL2012 and since then had operated 2,563 hours until the aforementioned leak had occurred, which resulted in the inoperative hydraulic system 1. The most common factors for gasket extrusion are pressure transients inside the pump casing, however there is no certainty as to what triggered the extrusion of this gasket.

During the approach to the SBBR landing, the crew, while continuing the emergency procedures provided for the hydraulic system 1 failure scenario, commanded the landing gear to be lowered by the alternating system. Main landing gears lowered and locked down. The doors of the nose landing gear unlocked, but didn't open. The nose landing gear unlocked but didn't lower down.

Research conducted on the lowering system of the nose landing gear and also on its doors, showed that the right door had restrictions on free movement. It was not possible to move the door hinges with natural hand effort. In the standard situation, it was expected that there was no restriction on the action to articulate the door, as it was found that there was no such restriction on the left door.

The resistance produced by the hinges, in the sense of articulating the right door, was greater than the force caused by the nose landing gear when driven by the alternating system. In case of activation of the alternating system, the effort exerted on the doors is only due to the weight of the landing gear, there is no hydraulic force for lowering the landing gear and opening the door.

Research conducted on the right door to find out what caused increased resistance to the hinges movement was not conclusive to the point of finding the determining factor.

It was identified that the hinges of this door had undergone structural repairs in September 2012, where there was the incorporation of larger radial pins and widening of the lobes orifices. The radial measurements of these pins and the lobe holes did not deviate from the predicted dimensions.

However, it could not be ruled out that any deviation or non-adhesion to the requirements established for the widening of the holes in the hinges regarding surface finish and corrosion protection could have been occurred.

In the same test, it was verified that the hinges showed no signs of recent lubrication.

However, despite the absence of signs of recent lubrication on the door hinges, it was found that all planned maintenance for the aircraft was performed as intended.

When the hinges were sectioned so that the internal relief of the surface of the lobes could be better observed, it was found that there was expansion of the superficial layers due to an oxidation and corrosion process.

In a normal condition, the lowering of the landing gear was controlled by the landing gear selector lever, located on the central instrument panel, and its movement occurred by the action of the hydraulic force provided by the hydraulic system 1.

At the moment when the lowering of the landing gear was commanded by the alternating operation selector lever, moving it to the extend position, what was in action at that moment to provide the lowering of the nose landing gear was only the effort on the doors caused by its weight.

It was found that the force exerted by the weight of the nose landing gear when leaning against the doors was not sufficient to overcome the resistance offered by the right door and result in its opening articular movement together with the left door, thus preventing the lowering of the landing gear.

It should be noted that the verification of the force required to articulate the right door hinges was performed after the accident, when the entire aircraft structure and the region near the nose landing gear had been subjected to unusual efforts.

In this sense, it must be considered that, due to the impact of the fuselage against the runway and subsequent dragging, the force to articulate the hinges could be lower, or even greater than the results found in the applied tests.

A progressive loss in alignment between the door and fuselage hinges, due to efforts resulting from normal aircraft operation, could also contribute to the pin working interfering with the hinge lobe holes.

The left door, although no resistance to its articulating movement was identified, did not open because its movement depended on the movement of the right door.

As could be seen, the doors were mechanically connected to each other. If one of the doors did not open, the other would not open either. The right door movement restriction, which originated from the hinge restriction, prevented the left door opening and it did not open either.

Considering the entire chain of events initiated by the failure of EDP 1 and the fact that all records of maintenance tasks were in accordance with the manuals in force established by the manufacturer, it should be noted that it was not possible to point out the determining factor that triggered the articular restriction of the right door movement hinges.

However, there may be some deviation, or non-adherence, in the execution of the inspection and lubrication requirements of the hinges. Consideration should also be given to whether there was any deviation, or non-adherence, in the fulfillment of the requirements established for the service of widening the holes in the hinges, especially those related to the coating and corrosion protection, and that this has made the joint area more susceptible to corrosive processes.

The possible deviations, or non-adhesions considered, could have resulted in increased resistance to the natural opening movement of the right door, resulting in the restriction of lowering the landing gear by the alternating system, where the effort produced to open the front doors occurred solely by the action of the nose landing gear assembly weight.

Related NOTAM:
J0200/14 - RWY 11R/29L CLSD TO AN INCIDENT. 28 MAR 23:45 2014 UNTIL 29 MAR 02:59 2014. CREATED: 29 MAR 00:16 2014