6. Hijack - It is also possible that the aircraft was hijacked to an unknown location. This possibility can be ruled out based on the following reasons:
- Skipping all the radars - when there are many country borders around the vicinity of the aircraft last point of contact, the aircraft is a big aircraft (radar cross-section of Boeing 777 would be bigger)
- Hiding the aircraft and passengers for 4 days,
- Using a runway/airport with no witnesses and
- No group claiming to have hijacked the plane
2. What kind of distress signal is expected when a crash happens? Will electrical failure affect the distress transponders or beacons?
Regulations require commercial civil aircraft to have Emergency Locator Transmitters (ELT). They are activated during a crash based on the G force they experience (gravity force) or by pilots input. Another beacon is attached to the flight recorder or the black box which is called Underwater Locator Beacon (ULB). The black box beacon is activated when it comes in contact with water.
Assuming the aircraft crashed on water, the ELT's would have sent signals, but they are not waterproof. The ULB starts emitting signals the moment it touches water.
Important facts to note:
- Although the aircraft might be emitting an automatic distress signal, there might not be anyone listening to them every minute. And these signals have a range within which there might not be anybody listening to them.
- The crash sometimes happens within a time frame of 15 minutes (AF447) and pilots may realize that a crash is imminent only 5-10 seconds before a crash. Only after 30 minutes to an hour, does the ATC realize that something is wrong and starts looking for the aircraft, by which time, the beacons are well underwater.
- The Under Water Beacon (ULB) can emit a signal for hundreds of miles. But if the black box is covered with debris or falls into a trench at the bottom of the sea, then the strength and range of the signal would be lower.
The ELT and beacons use their own batteries and electrical failure does not affect them.
3. Should the beacons run out of battery, what are the options?
The batteries of the beacons of the black box beacon are designed to last 28 days. If the black box beacon battery dies and the plane is not located within that time, then the only hope is to find the debris and try to work backwards from there on.
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