why does i.e. british airways flight 761GD called by ATC with "speedbird 761", and why do they have letters?

Answer 1

Some airlines have code names rather than the company names. For example, Airtran is called "Citrus" by ATC. It was Airtran's choice to be called citrus. Pan Am used to be called "Clipper".

The numbers next to it are the flight number. For example, a British Aiways flight number 1776 to Philadelphia would be called "Speedbird 1776"

A letter after the flight number is used to avoid confusion.

For example, suppose Delta flight 123 flies from Boston to Atlanta, and then continues to Los Angeles.

You have a Delta 123 from BOS to ATL, and a Delta 123 from ATL to LAX. Normally, there is no problem because 123 won't depart ATL for LAX until 123 arrives from BOS.

But today, there is a delay in BOS and flight 123 will be 2 hours late arriving to ATL. The Delta folks don't want to delay the 123 flight from ATL to LAX, so they call out a reserve crew to fly the ATL-LAX flight so it can leave on time.

Because of this, there will be two Delta 123 flights airborne at the same time which confuses the ATC computers. So, Delta assigns a letter after the LAX flight to avoid this ambiguity.

Now you have DL123 BOS-ATL and DL123X ATL-LAX or something similar. That's how it's done at my company.

Answer 2

Speedbird is the original callsign of BOAC. British Overseas Aircraft Corporation.
The European national airline at the time was BEA, British European Airways. Their callsign was Bealine.
These two airlines were merged in the 70's to form British airways, but the long haul side of the business still uses Speedbird and the Euro side of it uses Bealine.

Answer 3

I;m confused, do you mean ATC referred to it as "speedbird"? While flying I have heard ATC refer to some planes with "nicknames"

Once they cleared "big blue" and "the little one" to land when I was coming in behind an Air Canada flight, smaller airport - not like Heathro et al

I was the "little one" of course, Cessna Skyhawk