The problem with the MD-80 aircraft that provoked massive flight cancellations by American Airlines in March and April of 1980 concerned the wiring in the hydraulic systems. Because of a $10.2 million fine levied earlier in the month on Southwest Airlines by the Federal Aviation Administration for allowing aircraft to fly without proper inspections, American Airlines grounded its entire MD-80 fleet until the company completed inspections of the hydraulic wiring.
According to FAA regulations, the wiring bundles in MD-80 auxiliary hydraulic systems had to be spaced exactly 1 inch apart from each other, securely fastened to the wheel well of the plane and suitably covered. Although directives for the inspections were in a 38-page handbook, confusion by American Airlines engineers in carrying out the instructions led to the cancellations.
American Airlines grounded around 300 planes, which was its entire fleet of MD-80 aircraft. The airline cancelled about 2,500 flights in March and 3,200 flights in April. Across the United States, an estimated 100,000 passengers were stranded. The cancellations cost the airlines about $300 million in revenue. Although American Airlines spokespeople emphasized that the cancellations were not related to safety, their own pilots' union, the Allied Pilots Association, emphasized the FAA airworthiness directive about the hydraulic systems wiring bundles was warranted.