Who's Online

We have 1287 guests online

Live Traffic Feed

Life in the Skies

'A Local Bestseller!'

What Tony says
(See here)
and Book Launch video here
What others say

Les Posen

Yvonne Lee

Louisa Lim & Allan Koay

Aireen Omar, Asran & Bo Lingam

38 Readers' Comments
(See here)

Get an autographed copy here

AMAZON.COM  -  To Order, please Click here 

(eBook) Kindle edition - please Click here

Latest Comment

A successful SIA Cad
the deadline i guess it's the end of this februry,

Singapore Airlines P
Hello captain Lim , I am Ray . I would like

What are the eyesigh
sir i have -0.25 in my right eye and 0.75 in left

Spontaneous Pneumoth
I'm not a doctor or anything, @chinmay, so I can't

What are the cruisin
The idea that the earth is spinning is plain bulls

Singapore Airlines C
Hello Captain Lim, I am an Indian citizen, Engine

Spontaneous Pneumoth
my grandmother is 70 yrs. old also sugar patient.

Does a jet aircraft
From what I understood Flat earthers are just uned

A Boeing 777 can’t f
Aircraft airspeed systems measure how fast the air

When and how does th
I don’t know

Paperback Version

 For Local Availability - Check Here
Home > Air Travel > How planes are kept in contact with the air traffic controllers over the Ocean?
How planes are kept in contact with the air traffic controllers over the Ocean?
Flying - Air Travel
Tuesday, 15 July 2014 15:37

Funny ATC (VHF Communication) as President Obama Departs Boston

Hi Captain Lim,

I am flying from Toronto to London and I was wondering how planes are kept in contact with the air traffic controllers once over the Atlantic Ocean.

Thank you.


Hi Ryan,

The pilots of the planes are always in contact with the air traffic controllers (and the airlines personnel on the ground as well). Both of them are following and tracking the planes all the times.

How they go about doing that?

Well, various medium are used depending on where you are. The most common ones are the radios, either VHF or HF (Very High Frequency or High Frequency). VHF has a range of around 250-300 miles (based on line-of-sight range). It is very clear and used all along the route from Toronto to London as long as the plane is within 250 miles from any ground stations.

The distance of Toronto to London is around 3550 miles (5713 kilometers, 3085 nautical miles)

Once the plane is out of VHF radio range, then the pilot can use the HF radios. The HF does not depend on line-of-sight transmission but can follow the curvature of the earth. Although it has longer range, it suffers from night effect and become not very clear at times – so not a very good alternative.

Today most modern planes use more advanced communications (CPDLC, ADS, SATCOM – Google them for the technical explanations) to talk to the ground. CPDLC is quite similar to you using the SMS function of your phone.

Hence normal communication over the ocean is through text messages. However voice communication via the satellites (SATCOM) is also available. Since the cost of this communication is more expensive than text messages, SATCOM is restricted to urgent or emergency communications

Additionally, your plane from Toronto is also tracked all the way by radar as well as by ADS (Automatic Dependant Surveillance – a technology that allows the air traffic controllers to see traffic with more precision)

However, radar range is limited – similar to VHF radio range. Further tracking of the plane along the 3550 miles route would now be done by the ADS once radar coverage becomes unavailable.

So within the 250 miles when the plane is tracked on radar, for civil planes, this is performed with the transponder that allows the air traffic controller to see, for instance, how fast or how high the plane is flying at.

I believe there was some confusion on the understanding of the transponder operation in one recent event.

Could the transponder be switched off in flight?

Yes, it is possible. On the ground, this is done firstly to avoid cluttering up air traffic control radar when the plane is parked at the gate. It is then switch on shortly before taxiing out and then switched off again (on standby mode) after docking in at the next destination.

In case of an emergency such as a fire or electrical system problem, the transponder can be switched off (isolated) through a circuit breaker.

So the transponder, when it is in in the air, would provide all its function only within radar coverage. Once out of radar range, its function would be taken over by the ADS.

Hence, your trip from Toronto to London is within a call away from the ATC at anytime. Furthermore, your plane is positively tracked by the ground ATC as you passed by the various airspaces.

How Radar and Transponder work?


TrackBack URI for this entry

Comments (1)

Subscribe to this comment's feed
thanks for answering my question!
ryan , 10 Aug, 2014

Write comment

smaller | bigger


Paperback Version

 For Local Availability - Check Here

Recommended By..


'A Local Bestseller!'

Recommended by

Patrick Smith
Boston USA

Capt Meryl Getline
ex-United Airlines USA

Capt Doug Morris
Canadian Airlines

Capt  Robert J Boser
ex-United Airlines USA

38 Readers' Comments
(See here)

Get an autographed copy here

AMAZON.COM  -  To Order, please Click here 

(eBook) Kindle edition - please Click here

View Book Launch video here

Follow me


Like What You Read?

If you like what you read, more stories are found in my book LIFE IN THE SKIES (Preview here) and you can purchase a copy here. To check for any latest updates or postings, you can follow my Twitter at @CaptKHLim or Facebook here

MH 370 Interviews

Click here to View

10 Most Popular Posts

Disclaimer | Privacy
2004 - 2011 © AskCaptainLim.com | Site Concept by eQuilec.com