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.
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