Thielert Engine Owners Group Alerts Members

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 its decision:

• 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 in flight."
• 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 engines."

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 fuel."

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 fueling.

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."

The full .pdf document is available here.

FMI: www.exxonmobil.com, www.thenog.org