Missing Malaysia Airlines Flight MH370 Q&A: How could something just disappear?

Ian Johnston explains some of the technology involved in modern aviation, and why it may be far from infallible

Why doesn't air-traffic control cover the entire globe?

Air controllers generally use so-called "secondary radar". This sends a signal to a plane's transponder, which then replies with a "squawk" that identifies the flight and shows its position. However radar is limited by line of sight -a plane behind a mountain would not receive the outgoing signal - so it is affected by the curvature of the Earth. Radar signals are also dispersed by the atmosphere, so they get weaker as the target gets further away. Eventually the signal is lost. However there are plans to introduce satellite flight-tracking, similar to Global Position Signals or GPS, covering most of the Earth by 2020.

What about other kinds of radar?

"Primary" radar, which is used mostly by the military, is basically the same as the original 1930s invention. It sends out a signal, which reflects off objects - metal works particularly well - and bounces back. Planes and other objects can therefore be tracked whether they want to be or not. However, it has the same limits of line of sight and atmosphere. The curvature of the Earth means an aircraft would have to be at more than 30,000ft to be picked up 250 miles away, but radar signals tend to get patchy at distances of 100-150 miles.

Why do planes travel along 'corridors' or 'airways'?

'Airways' are suggested routes given to planes by air-traffic control. They might be about 10 nautical miles wide and with an altitude range within which the plane should stay. They are designed as navigational aids and pilots can deviate from their airway with permission from air-traffic control. "Corridors" are defined flight paths set up by governments and military authorities to restrict flights for a particular reason - flights during the West Berlin airlift were restricted by the Soviet bloc in this way.

How much space does a plane of the 777 size require to land?

It depends how heavy it is. A 777 that was almost empty of fuel would need a mile or so, less than half the length of Heathrow's shorter runway.

If the US government can read my emails, why can't the mobile phones be tracked?

Mobile phones are essentially small radios and any transmission can be triangulated to establish the point of origin. However, in order to be small enough to fit into your pocket and not run out every few minutes, mobiles were designed to use only a small amount of power and have small antennas. This limits the range severely, much like a walkie-talkie, to about 25 or 30 miles, depending on atmospheric conditions.

 

I thought black box recorders always gave off a signal?

The black box is a flight recorder and planes generally have two. One records flight data from the plane's instruments, the other records conversations in the cockpit. If it goes underwater it will emit an ultrasonic signal, but this only has a limited range. Planes have three main means of communicating with the outside world: the pilots' high-frequency radios, the Acars data-transmission system, which enables the flight's computers to talk to computers on the ground, and the transponder, which sends the ID squawk to secondary radar and handles the aircraft's emergency distress button.

Do all planes have an emergency distress button?

All aircraft operating under the regulations of the International Civil Aviation Organisation must carry and register their distress beacon. A radio frequency - 121.5 Mhz - is reserved for emergency communications from civilian aircraft and is monitored by air-traffic control centres, emergency services and other aircraft.

Suggested Topics
Start your day with The Independent, sign up for daily news emails
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Business Analyst - 12 Month FTC - Entry Level

£23000 - £27000 per annum: Recruitment Genius: A Business Analyst is required ...

Recruitment Genius: Chefs - All Levels

£16000 - £23000 per annum: Recruitment Genius: To succeed, you will need to ha...

Recruitment Genius: Maintenance Engineer

£8 per hour: Recruitment Genius: This is an opportunity to join an award winni...

Recruitment Genius: Telesales Executive & Customer Service - Call Centre Jobs!

£7 - £9 per hour: Recruitment Genius: Are you outgoing? Do you want to work in...

Day In a Page

Greece debt crisis: EU 'family' needs to forgive rather than punish an impoverished state

EU 'family' needs to forgive rather than punish an impoverished state

An outbreak of malaria in Greece four years ago helps us understand the crisis, says Robert Fisk
Gaza, a year on from Operation Protective Edge: The traumatised kibbutz on Israel's front line, still recovering from last summer's war with Hamas

Gaza, a year on from Operation Protective Edge

The traumatised kibbutz on Israel's front line, still recovering from last summer's war with Hamas
How to survive electrical storms: What are the chances of being hit by lightning?

Heavy weather

What are the chances of being hit by lightning?
World Bodypainting Festival 2015: Bizarre and brilliant photos celebrate 'the body as art'

World Bodypainting Festival 2015

Bizarre and brilliant photos celebrate 'the body as art'
alt-j: A private jet, a Mercury Prize and Latitude headliners

Don't call us nerds

Craig Mclean meets alt-j - the math-folk act who are flying high
How to find gold: The Californian badlands, digging out crevasses and sifting sludge

How to find gold

Steve Boggan finds himself in the Californian badlands, digging out crevasses and sifting sludge
Singing accents: From Herman's Hermits and David Bowie to Alesha Dixon

Not born in the USA

Lay off Alesha Dixon: songs sound better in US accents, even our national anthem
10 best balsamic vinegars

10 best balsamic vinegars

Drizzle it over salad, enjoy it with ciabatta, marinate vegetables, or use it to add depth to a sauce - this versatile staple is a cook's best friend
Wimbledon 2015: Brief glimpses of the old Venus but Williams sisters' epic wars belong to history

Brief glimpses of the old Venus but Williams sisters' epic wars belong to history

Serena dispatched her elder sister 6-4, 6-3 in eight minutes more than an hour
Greece says 'No': A night of huge celebrations in Athens as voters decisively back Tsipras and his anti-austerity stance in historic referendum

Greece referendum

Greeks say 'No' to austerity and plunge Europe into crisis
Ten years after the 7/7 terror attacks, is Britain an altered state?

7/7 bombings anniversary

Ten years after the terror attacks, is Britain an altered state?
Beautiful evening dresses are some of the loveliest Donatella has created

Versace haute couture review

Beautiful evening dresses are some of the loveliest Donatella has ever created
No hope and no jobs, so Gaza's young risk their lives, climb the fence and run for it

No hope and no jobs in Gaza

So the young risk their lives and run for it
Fashion apps: Retailers roll together shopping and social networking for mobile customers

Fashion apps

Retailers roll together shopping and social networking for mobile customers
The Greek referendum exposes a gaping hole at the heart of the European Union – its distinct lack of any genuine popular legitimacy

Gaping hole at the heart of the European Union

Treatment of Greece has shown up a lack of genuine legitimacy