It was an 'APU fire warning' that forced a Singapore-bound Air India flight from Delhi, carrying nearly 200 passengers, to return to the national capital early on Thursday morning.
Passengers aboard the Boeing 787-9 Dreamliner operating the AI 2380 had been nearly airborne for an hour, before the flight safely returned to Delhi due to the "APU fire warning", as per a PTI report.
The passengers were transferred to another flight headed to Singapore, as the airline apologised for the technical snag.
What is an 'APU fire warning'?
According to the International Civil Aviation Organization (ICAO), the UN's civil aviation body, an Auxiliary Power Unit (APU) is a small self-contained power unit on an aircraft providing electrical/pneumatic power to the aircraft's systems during ground operations.
Indeed, its primary use is during ground operations, because it allows for a number of functions—from starting the engine and maintaining optimal cabin conditions to powering various parts of the aircraft.
However, in the air, a certified APU's main function is to provide backup power in case an engine generator fails.
Since APUs deal with powering various parts of the flight, fire warnings—despite the fire-proof materials that these components are built with—for these are a big deal.
This is because on the ground, they present a risk of explosion and possible airport infrastructure damage—which could even escalate to injuries and deaths.
APU fire warnings are a bigger concern when reported mid-air, not only because of the possibility of an explosion and deaths, but also because the flight would be left with just its main power—which does not necessarily imply a disaster, but is still a huge risk.
