Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all McDonnell Douglas Model MD-90- 30 airplanes. This proposal would require replacement of the starter relay of the auxiliary power unit (APU) with a new, improved relay. This action is necessary to prevent failure of the APU starter relay, which could result in depleted main airplane batteries, overheated APU starters, and damage to the wiring adjacent to the APU starter. This action is intended to address the identified unsafe condition.