Airworthiness Notice - B021, Edition 1 - 18 November 1994
Low Temperature Operations with Jet a Fuel
(This Airworthiness Notice supersedes N-AME-AO 07/89)
( dated 26 January 1989)
The year-round use of Jet A fuel has been an ongoing discussion topic within the Canadian General Standards Board (CGSB) Committee on Aviation Fuels for some years. In 1987 a joint CGSB/Transport Canada Cold Fuels Task Force was formed to evaluate the situation and, as a consequence, N-AME-AO 07/89 was issued to alert operators of the possible safety implications. This Airworthiness Notice supersedes N-AME-AO 07/89 and updates the information contained therein.
Jet A, with a specification Freezing Point of -40oC, is not intended for use during extremely cold weather conditions or where the ambient temperature is close to, or below, -40oC. Operational experience shows that aircraft fuel tank temperatures can approach that of the ambient conditions in as little as three hours for a business jet and six hours for a large transport category aircraft. Although lower, slower commuter aircraft are not exposed to the same ambient temperature extremes for the same length of time, they could still encounter similar fuel temperatures during flight if they have uploaded pre-chilled fuel.
The consequences of low fuel temperatures are an increase in viscosity and the eventual formation of wax crystals. The increased viscosity could result in adverse changes to the engine fuel scheduling, while an excessive wax accumulation could cause filter blockage, fuel pump performance degradation or difficulty with transfers between tanks. If corrective action such as a change of altitude or increase in speed is not taken, there could be a complete loss of power or an aircraft balance problem.
The CGSB Committee on Aviation Fuels has alerted Transport Canada Aviation to the fact that Jet A-1, the preferred fuel type for adverse climatic conditions, is less likely to be available than Jet A. In addition, both Jet A and Jet A-1 are being manufactured close to the respective Freezing Point Limits of -40oC and -47oC.
Operators having aircraft which do not have fuel temperature gauges and corresponding flight manual limitations are strongly recommended to use only Jet A-1 fuel when penetrating low temperature air masses and to, in any case, assume that the fuel temperature is at the ambient air temperature after three hours in flight.
From the above, there is an implication that there may be some erosion of existing safety margins for certain aircraft operations, particularly those involving aircraft that do not have fuel tank temperature indication, or where older aircraft flight manuals are not specific on the matter of cold fuel and the associated operating procedures.
As a consequence, Transport Canada strongly recommends that operators ensure that flight crews have an adequate awareness of the potential risks and the inadvisability of using Jet A fuel when extremely low ambient temperatures are likely to be encountered.