Squawk 7700?

[Will]

Hi everyone, a question for our real-world aviators.

I've been playing with FlightRadar24, an app with a zoomable map that shows you the location of every ADS-B equipped aircraft in the entire world. Just for fun, it can also send you an alert any time an aircraft squawks 7700 (emergency).

Just the other day, I watched this happen in real time: http://avherald.com/h?article=49d09a27&opt=0

Got the text alert, located the aircraft, watched them circle twice while drifting down, and then level off at 3000 feet for final vectors to the ILS at Lyon. Fun to observe. AvHerald had the story up the next day.

Right now, as I type this, British Airways 677 from Istanbul to London is squawking 7700, and descending through 8000 feet midway between Budapest and Vienna. Looks like something is up, but no details available yet.

In those two cases, it looked like the crew noted an irregularity and initiated a diversion. Sometimes though, an aircraft will squawk 7700 and not change altitude, not divert, and then after a few minutes go back to using another non-emergency code.

My question is this: other than declaring an emergency, what are some reasons to squawk 7700? 

[Michael Benson]

Hi Will,

The use of 7700 from an ATC point of view is to alert other sectors/units immediately that the aircraft may do manoeuvres which are not expected, whether this to be descending/climbing, change of heading, route through their sector even though not planned, etc. 

The other advantage is that aircraft sqw-ing 7700 tend to be highlighted, flash, etc which makes it much easier to co-ordinate rather than trying to point out where it is; especially as most modern ATC radars filter a significant amount of traffic.

The severity of the incident isn't always indicated by the choice of squawking 7700, I've had sick passengers land on a 7700 whereas a 777 with a massive hydraulic failure without.

I have to say I find more and more crew less receptive to sqw 7700 due to these very sites and the impending "terror in the skies" headlines in the Sun the following day!

[tango4]

Well, I don't really see any reason apart from an emergency. The exact cases where pilots will or will not squawk 7700 will mostly depend on airline policy and on the pilot. But as a rule of thumb, MayDay implies squawk 7700.
The only other case (although a related case) that I can think of where a pilot will squawk 7700 is when requested by ATC. Sometimes, a pilot will declare an emergency without using this code, for example for a medical emergency. In that case ATC might request that the pilot squawk 7700 to ease coordinations between control facilities (enroute center, approach, tower...). If the aircraft is using this special code, it will be easier to spot on every ATC screen because you usually have a colored label on it, and it forces the visualization of this aircraft even if it is not supposed to go through your sector (for example in case of diversion). And thanks to Mode S transponders, now you retain the correlation (meaning the radar blip is still associated with its flight plan).
Don't know if that is the type of answer you were looking for but I hope it helps a bit.


Charles

[tango4]

Woops I guessed our answers crossed !
At least we are basically saying the same thing !