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Why would pilot switch off transponder? Good question

March 17, 2014 Aviation, Headline News No Comments Email Email

egtmedia59Conjecture about what happened aboard missing Malaysia Airlines flight MH370 will continue forever – unless the plane suddenly turns up, an eventuality that seems extremely unlikely.

Whoever it was that was controlling the plane after it suddenly disappeared from radar took a series of steps to disable communication, as far as they could.

It must either have been the pilots (or one pilot who overcame the other) or a third party who gained unauthorised access to the flight deck and either forced the pilots to do their bidding or flew the plane themselves.

Doors to flight decks have been strengthened, made more secure and bulletproof, since the terrorist attacks on New York on 11 September 2001. Those attacks were carried out by terrorists who gained access to the cockpit. Yet cockpit doors are opened numerous times during the flight, as pilots take toilet breaks and stretch their legs.

The doors open about eight times during an average flight, one analyst worked out, and while cabin crew are supposed to stand guard whenever that happens, they are often too busy to do so, or are distracted from the

After the 9/11 attacks, observers warned that the simple manoeuvre of switching off the planes’ transponders had made them harder to track. A transponder is a type of radio or radar transmitter/receiver that transmits signals automatically when it receives predetermined signals.

Why would any pilot want to switch it off, other than for a sinister purpose? Perhaps transponders on aircraft should be impossible to turn off.

Pilots, however, report that transponders on rare occasions go haywire, or even short circuit, trip circuit breakers or otherwise misbehave.

“It’s imperative in these cases that pilots have control over the power supply to any equipment in the aircraft,” one pilot wrote in a pilot’s forum.

Another idea is to have transponders that can be turned back on remotely, from the ground, in an emergency. Some safety experts, however, warn that would actually add to the risks. If someone could hack into a signal and override the pilots, they could potentially crash a plane without even being on it.

According to a Wall Street Journal report, MH370 kept sending signals without content through the Aircraft Communications Addressing and Reporting System (ACARS) for four hours after the last radar and radio contact. ACARS is a digital datalink system for transmission of short, relatively simple messages between aircraft and ground stations via radio or satellite.

ACARS indicates that the B777’s engines continued to run throughout that period. The Malaysian Government has now confirmed that the plane flew for hours after changing course.

A report in Aviation Weeks says that, eventually, all commercial aircraft will stream live-status data directly to operation control centres, “offering real-time situational awareness that is all but non-existent today”.

The key will be to get the airlines to invest in such equipment, given that incidents like MH370 are profoundly rare, if not unique.

“Malaysia, like most other airlines, has not invested in a system that supplements standard aircraft-status-reporting channels such as air traffic control or ACARS – a data link using VHF, HF or satcom over oceanic airspace whose messages are routed via ground stations to the end users,” Aviation Week observed.

Written by Peter Needham

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