Airworthiness Notices - B048, Edition 1 - 11 December 1998

Hazards of Incorrectly Identifying or Mixing Aircraft Fluids


This notice is issued as a reminder to all personnel involved in the maintenance and servicing of aircraft. It stresses the importance of taking appropriate measures to ensure that correct fluids are used and that fluids of different specifications are not mixed, while servicing aircraft systems.


The mixing of hydraulic fluids in an aircraft main and brake systems, may have been a contributing factor in a recent fatal accident. Numerous other documented incidents have been directly or indirectly caused by the use of incorrect fluids, or by the mixing of different fluids having different specifications. The actual number of these incidents may be significantly greater than the number reported. The dangers associated with the mixing of fluids are present in all segments of the aviation community, whether commercial, corporate, executive or private.

Vulnerable Systems

Several aircraft systems are vulnerable to fluid misidentification. Hydraulic, brake, wheel, fuel, anti-detonation and de-icing systems are especially vulnerable to these errors. In the case mentioned above, the hydraulic fluid MIL-H-5606 was inadvertently mixed with MIL-H-83282. The two fluids have a similar appearance, but different flash points. There are numerous other such potentially hazardous situations. Consequently, the personnel involved in the maintenance of aircraft must remain vigilant. It is not adequate for the specifications and any changes made to them to be simply published. It is of the utmost importance that the responsible managers and supervisors ensure that personnel involved in the maintenance and servicing of aircraft systems, are not only provided with the initial training, but are made aware of changes and, importantly, of the reasons for these changes.

Some of the more common fluids that are particularly prone to misidentification are listed below, along with the fluids with which they may be confused:

  • Hydraulic fluids (different specifications, mineral vs phosphate ester vs vegetable base)
  • Engine oil (different viscosities, detergent vs non detergent types, mineral vs synthetic base)
  • Fuel (different octane ratings, gasoline vs turbine fuel)
  • Anti-detonant (water methanol or distilled water vs plain water or fuel)
  • Nitrogen (vs compressed air)
  • Aviation oxygen (vs medical oxygen)
  • De-icing, anti-icing fluids (different viscosities, different base)

These are just some of the fluids that are prone to misidentification. Following are some facts that affected personnel should always be conscious of, and precautions that should become habits:

  • Incompatible fluids can adversely affect systems components, i.e. hoses, seals, etc.
  • Complacency is hazardous
  • Appearances are deceiving
  • Identification on packaging should not be taken at face value, but confirmed by other factors
  • Always ensure that the product specification is the applicable one
  • In the case of aircraft fueling, challenge the operator in respect of the content of the delivery vehicle
  •  Beware of products identified by means of generic storage
  • Never use the content of unmarked dispensers

For Minister of Transport

D.B. Sherritt

Director, Maintenance and Manufacturing