There are several type of jet propulsion system. Steam jet engine is the most common and runs on water and coal. The gnomes' more advance whizbang engine runs on petrol. Petrol is very flammable and combustible substance closely associated with greek fire.
Jet engines have an average SR of 6. The SR can be raised up to the maximum of SR9 by customizing the engine by an expert rated mechanic, magical enhancement or special built engine (treat as magical item creation). SR decreases by one per additional 2 tons added to the load. There is a 5% chance of break down for every hour the engine is run on maximum SR beyond SR6. There is a cumulative 1% chance of breakdown if daily maintenance is not performed correctly (roll 1 on d6) added to chance of breakdown. The engineman can repair minor break down (10% or less) if he has the Repair Engine NWP. For every additional hour spent to repair the engine lessen by 1% the chance of another break down. A mechanic is needed to repair any any break down above 10%.
Non-weapon Proficiency: Repair Engine (Int -1) Allows to repair non-magical mechanical engine used in spelljamming ships.