Background
During taxi for departure of a Boeing 767, the flight crew observed 'R GEN OFF' and 'R GEN DRIVE' EICAS messages, indicating a malfunction of the right integrated drive generator (IDG). The aircraft returned to the gate, and maintenance was notified. A mechanic was dispatched to the aircraft.
Maintenance Response
The mechanic reported that he had assumed the crew had disconnected the IDG. The captain stated that he was advised by the mechanic that the IDG was disconnected. The aircraft was subsequently prepared and released under its Minimum Equipment List (MEL) for the flight, utilizing the left IDG and APU generator.
In-Flight Event
During climbout, a 'R STARTER CUTOUT' EICAS message illuminated, followed by a fire warning on the right engine. The flight crew exhausted both fire bottles, after which the fire warning extinguished. The aircraft returned to Salt Lake City for an emergency landing on runway 16L.
Post-Incident Examination
Examination of the engine revealed the fire-damaged remains of the right IDG and its magnesium housing. A download of digital data from the aircraft indicated that the original EICAS and IDG annunciations were related to low oil pressure within the IDG. An FAA inspector, who examined the aircraft immediately following the event, found the right IDG disconnect switch still safety wired, meaning the IDG could not be disconnected without breaking the wire and depressing the switch.
MEL Procedure
Investigation revealed that the MEL dispatch procedure developed by the carrier did not address the need to run the associated engine at or above idle in order to successfully disconnect the IDG.