It's a shot across the bow for owners of diesel-powered
aircraft. In a letter sent by ExxonMobil US General Aviation
Operations Manager Martin Tippl to distributors of Jet-A fuel on
November 17, the company announced it has made the technical
decision that ExxonMobil Aviation does not support or endorse the
supply of jet fuel to aircraft powered by diesel engines.
Included with the letter is an Indemnity Agreement, to be
completed by suppliers and returned to ExxonMobile, prohibiting the
supply of jet fuel to diesel-powered aircraft and releasing
ExxonMobile from any liability in the matter.
In the letter, ExxonMobil details three technical reasons for
Ignition Quality- "The fact that the minimum
cetane required to establish airworthiness has not been determined,
in combination with the fact that cetane is not measured as part of
the jet fuel specification, means that ExxonMobil cannot guarantee
the ignition performance of the jet fuel it supplies and cannot
know if the aircraft will be airworthy after fueling."
Freezing Point- "Unlike turbine powered
aircraft, piston powered aircraft do not reach speeds that cause
heating of the fuel in the wing due to friction caused by airflow.
It is therefore possible that an aircraft powered by a diesel
engine could reach altitudes where the fuel would begin to freeze
Lubricity- "Diesel engines rely on the fuel to
lubricate key components of the fuel injection system. ExxonMobil
Aviation cannot guarantee that the lubricity performance of the jet
fuel it supplies will meet the requirements of aviation diesel
ExxonMobil states that "until such time as the Federal Aviation
Administration and the aviation fuel industry has a clearer idea of
the full effects of these issues, the ExxonMobil Aviation position
is that diesel powered aircraft should not be fueled with jet
The letter does not expressly state ExxonMobil will refuse to
fuel diesel-powered aircraft... but does make clear that customers
who insist on being fueled with Jet-A do so at their own risk.
Customers insisting upon purchasing jet fuel for their diesel
engine aircraft must sign an indemnity agreement before
The letter concludes, "No fueling of diesel engine aircraft with
jet fuel may be performed without a valid indemnity agreement
signed by the customer in place."