Airbus is testing a health-monitoring system for A320 avionics bay fans that have been triggering in-service issues, including diversions, due to premature bearing failures.
Word of the system comes in an Air Accidents Investigation Branch (AAIB) report an EasyJet A320 diversion this past January. The aircraft, 1.5 hrs. into a flight from Paphos, Greece, to London Gatwick, was diverted to Athens when the flight crew detected a “whirring noise,” vibration from below the cockpit, and “a distinct electrical burning smell,” the AAIB report details. The culprit: a seized cooling extractor fan due to a bearing failure.
Airbus and supplier UTC Aerospace Systems (Hamilton Sundstrand) have introduced improvements, including swapping ceramic bearings for the original steel bearings.
“Despite the change to ceramic bearings, although better than the conventional bearings, they remain the parts in the fan assembly which tend to wear first and are the main failure mode,” AAIB explains.
As a result, Airbus and UTC in 2013 recommended reducing the overhaul interval to 10,000 hours.
The EasyJet fan that failed had ceramic bearings and 25,700 hrs. in service.
asyJet, which is working with Airbus to develop predictive maintenance services on the A320 family, instituted its own program to identify “high-risk” fans using a mix of its own in-service data and OEM recommendations, AAIB says. EasyJet identified 131 fans and had removed and overhauled about 80 of them—at a rate of about 15 per month--at the time of AAIB’s report.
"In addition, the operator will be participating in an in-service evaluation of a fan health monitoring unit,” AAIB adds. "This equipment is designed to monitor vibration levels to give an early warning of possible bearing failure and to shut the fan down automatically when very high vibration is sensed to avoid critical failure that leads to smoke or burning smell events.”
The EasyJet incident is the second A320 cooling fan failure anomaly investigated by AAIB in the last two years. An earlier incident led to a British Airways A320 declaring an emergency as it approached London Heathrow in July 2015.