Avgas fuel contamination event 1999

The Avgas contamination event that happened over Christmas 1999 caught everyone by surprise. It had not been seriously considered as a potential hazard to aviation anywhere in the world, therefore the consequences had not been considered. The reasons behind why the fuel became contaminated were unexpected. Mike Watson, one of a team of transport safety investigators who had the task of sifting though an overwhelming amount of data and publishing the final report, gives some insight.

No one was hurt as a result of contaminated aviation fuel, and there were no accidents that could be attributed to a loss of power caused by fuel contamination. At the time of the crisis the fuel refiner responded immediately and recalled all Avgas that had been manufactured at the refinery, and CASA grounded all Avgas powered aircraft that could have been contaminated until it was known that they were safe to fly.

The chemical contaminant is now known to have been ethylene diamine. At the time of the event, there was a concerted effort to define what the contaminant was (concentration in the Avgas was low); how the contaminant had got there; and what the contaminants behaviour would be in an aircraft fuel system.

In the initial response a method to guarantee aircraft would be safe again was developed, and a testing process to detect ethylene diamine was also developed in a number of weeks. Components for the test kits were sourced from all over the world.

The ATSB's investigation looked at what had happened. It looked at what could have prevented it from happening and why it didn't. It also looked at lessons that could be learnt and applied to other aviation systems. This included what would have happened if a similar contamination event occurred in a large turbine-engine passenger aircraft operating with contaminated jet fuel.

The main defence against any safety-critical system failure in an airliner is to have backup, or redundant, systems for any system that is essential for safe flight. The problem with fuel storage and supply systems in an aircraft is that they simply don't have a redundant backup. If fuel is contaminated, the contaminant will be supplied to all an aircraft's engines at the same time, and could make them all unreliable at the same time.

As the primary defence of a redundant system isn't available to protect against the safety critical problem of fuel quality, we could reasonably expect there to have been a number of fuel quality related accidents in the recent past; however that was not so. This can only be attributed to a highly reliable system for manufacture and distribution of aviation fuels, with a well-managed quality control processes.

Despite this, it is clear that complacency on the part of any group that has a responsibility towards maintaining fuel quality, be they refiner, distributor, regulator or consumer, can have catastrophic consequences.

This Avgas contamination event must be seen as a clarion call to highlight an aspect of the system of safe aviation that is more vulnerable to abuse or neglect than most other safety critical aviation systems.

Avgas contamination investigation report released

The Australian Transport Safety Bureau (ATSB) released its report on the contaminated aviation gasoline (Avgas) investigation at a media conference on 30 March 2001. The investigation followed the grounding in January 2000 of thousands of piston engine aircraft across eastern Australia when a black gunk was found in fuel systems.

The investigation found that a very small amount of an anti-corrosion chemical that was not removed in Mobil's Avgas refining process in late 1999, and not detected by the usual tests, led to the safety problem.

The ATSB made 24 separate recommendations as a result of its investigation that included recommended safety actions for Mobil Oil Australia, US and UK fuel standards bodies, the Civil Aviation Safety Authority, and other Australian regulatory organisations.

ATSB Executive Director Kym Bills told the media that the scale of the Avgas contamination was an unprecedented event anywhere in the world and was unexpected in such a mature industry as fuel refining. As a result, it caught the refiner and regulators by surprise and also revealed deficiencies in international fuel standards.

The investigation found that a temporary variation in the production process at Mobil's Altona refinery in late 1999 involving problems with reduced caustic wash and increased acid carry over, led to an increased dosage of an alkaline anti-corrosion chemical by a contractor. This was not totally removed from the final Avgas. The normal tests for the quality of Avgas did not pick up the very small concentration of the chemical contaminant in the Avgas that was sufficient to react with brass in aircraft fuel systems and form a black gunk that clogged them.

Mr Bills said it was not the ATSB's role to ascribe blame to any party. The task was to uncover the facts including all of the significant contributory factors (including weaknesses in defences), and then to publish findings and recommendations in a report.

Accordingly, it was important that relevant parties learnt from the identified safety deficiencies and acted promptly on the 24 recommendations made to reduce the chances of a recurrence, either with Avgas or jet fuel.

Type: Educational Fact Sheet
Author(s): Mike Watson
Publication date: 8 October 2000
Related: Fuel
Last update 18 March 2016
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