Airworthiness directives are the continuing operational safety system working exactly as intended. This article does a lousy job of mixing ADs with ordinary operational issues and even ground handling problems.

All airplanes have ADs over their life, and not all ADs are created equal. Some only require action once, and others have a recurring action. Some require simple inspections, while others require invasive testing and repair. Some have long compliance timelines (potentially years) while others are "before further flight." An airplane is not airworthy unless all active ADs have been complied with, so airlines must make sure that happens. The raw number of ADs issued for a given aircraft type in a given time period isn't a good metric for anything.

Dispatch reliability is a bigger day-to-day concern for airlines and passengers. After all, you want to get where you're going, and the airlines want to get you there. Poor dispatch reliability means the airline needs to accommodate (and maybe compensate) passengers and recover from the busted schedule. That recovery is harder with an A380 because of the large number of affected passengers.

Some of the aircraft engines in the piston GA fleet can tolerate lower-octane unleaded gasoline such as mogas without modifications. The Experimental Aviation Association has developed an STC that that permits the use of mogas in some combinations of aircraft and engines. Several popular engines, such as the Continental O-200 used in the Cessna 150, are on the list.

I fly a Cessna 150, and we have applied the EAA STC to our aircraft. Mogas can work just fine for normal operations and it's cheaper than avgas, but we run straight avgas after we've done certain types of engine work that require a break-in.

The real issue is that most of the avgas burned today is used by aircraft that have engines with large-bore cylinders and high compression ratios. They need the higher octane rating to prevent knocking. Engines like the Continental IO-550 have compression ratios of 8.5:1 or more.

Additionally, consider that all of the components of an aircraft's fuel system need to be evaluated. The fuel tanks, hoses, gaskets, pumps, valves and everything else need to be considered. A replacement fuel cannot have any adverse impact on the engine or the rest of an aircraft's fuel system. Performance with any replacement fuel must also be evaluated.

As for a replacement, if it eats away at the seals (like mogas with ethanol), it's unsuitable. If it shaves too much off of an aircraft's performance due to reduced power output or a weight difference, it's unsuitable. If it doesn't work with existing fueling infrastructure, it's unsuitable. If it costs too much to produce, and therefore will be far more expensive than what we have today, it's unsuitable.