Emergency Descent

[The Real Slim Shady]

I guess that this could be posted in Questions (purist police alert) but I wanted a sensible debate rather than just loudmouthed pilots shouting the odds, so post it here.

The process for the Emergency Descent (737) involves 2 events which affect you, the controller, and I would like to know your slant on these and whether one course of action is preferable over another.

Firstly, ICAO mandates a 90 degree turn off the airway as part of the procedure.

In a low density traffic area the turn wouldn't make much difference to other traffic but over London, Amsterdam, Brussels, Paris, Frankfurt etc it could cause some grief:particularly if you have to wait to find out which direction the turn has been made in. As an aside the Fokker procedure is a straight descent.

From a working viewpoint do you prefer a straight ahead descent or the crew following the ICAO guideline?

Next, the issue of squawking 7700: is it more prudent to retain the current squawk assigned by ATC until instructed by ATC to select 7700, or to change over straight away?

What effect does a 7700 immediate change have on your display? Will you lose data tags? Is an immediate change more of help or a hindrance?

Thanks guys and gals.

[Lookatthesky]

From my 'working viewpoint' I would not wish to see you turn 90 degrees left or right, and I guess from your viewpoint, if it's an emergency descent, the last thing you want to be worrying about is making a turn!!!

7700 is 'the best' thing that you can do ASAP as it alerts everybody sitting in front on a radar that you have a problem. More importantly, if 7700 is seen coupled with a quick descent, we will do everything to get those beneath you out of the way, which takes me back to point 1. I you're just descending in a straight line, that makes track projection and the 'clearing of a path' far easier, if you start turning however.......

As an aside, if faced with such a scenario, it would of course be nice to know that you are able to make turns, as this would make it easier to ensure your safety on the way down.

[Not Long Now]

If you're going to be doing things we're not expecting, getting 7700 on as soon as possible could well be a life saver! It will force through any filters on my radar and I can start getting things out the way.
As for turning 90 degrees, as you say, might be of some use if you're on an airway but in a TMA would probably just cause more confusion in our ranks.

[5milesbaby]

Also if a pilot makes a 90 degree turn, in the situation they're under will they select direction of turn toward the more suitable aerodromes for landing should they need to get on the ground ASAP? I doubt they would have time to even consider this.

I know that UK Area and Terminal centres retain the datablock with callsign and have a box flashing around them should you select 7700. Depending on which emergency Sq you select (7500/7600/7700) our third line of the box is filled with either HIJK/RTF/SOS so we know which ones selected. At Swanwick the box around the callsign flashes red and yellow. I don't know about other European centres wether the callsign is retained, but I'd imagine that there are a great number that do.

Personally, I'd want you to continue in a straight line and get 7700 going ASAP.

[ukatco_535]

I work in the TMA and am with 5milesbaby with this.... if you happen to need an emergency descent when you are whizzing about in the upper levels of the TMA or just after transfer to en route, a 90 degree turn is the last thing we would want.

We do not bother with airways in the TMA due to airspace limitations so the chances are you will be on an assigned heading anyways even after transfer to en route (until they have had a chance to sort out the mess we hand them and put you back on 'own nav').

Squawk emergency straight away if you can - it's one of the first things we would ask you to do when you declared an emergency with us - there is no box around your squawk at TC, but it does flash with the relevant emergency code, as per 5milebabys post, and we do retain the ident as well.

The squawk is the most important thing here - as soon as you show an emergency squawk, ATC will endeavour to get other A/C out of your way.... a turn by yourself may put you into confliction elsewhere, and although to turn is an ICAO standard, it is an unusual enough situation that the ATCO may get thrown by it.

We are too busy to continuously monitor an individual flight (until it declares an emergency, then priorities change), so we do not expect you do deviate unless you ask - hence why we get shirty if pilots turn due to weather before asking... it's inherently dangerous :)

[The Real Slim Shady]

Thanks for the replies folks.

The turn is mandated in the Boeing 737 procedure but not by Fokker. I tend towards favouring the straight descent so that you guys can track predict as the turn can be tricky to predict. For example, heading south east towards the Alps I would prefer to turn right: heading north west turn left.

However, the trun on the MCP altitude selector would be anti clockwise i.e twisting it to the left. The natural response would likely be to twist the heading selector in the same direction so the turn would likely be to the left.

The advantage of the turn is that the wing going down encourages the airplane to enter the descent; the manouevre is carried out on autopilot and the G profile for a descent is normally a 0.25G entry which is very gentle. Dropping the wing improves the rate of entry.

The importance of the 7700 squawk is interesting; I will flag that up to my colleagues.

Turns are not a problem once we have 2 way comms via the O2 masks - the noise may be a problem due to the continuous flow of O2.

If you can provide an MSA, if it is above 10000ft and a regional QNH that helps us too.

Thanks again guys.

[Tarq57]

Obviously a decompression is a serious business- as much for "what caused it?" as the fact of having an unsurvivable atmosphere on board. While the ATC (self included) view of straight ahead is preferrable, the most important thing is what's best for the aircraft. In and emergency situation we tend to manage by thinking -real fast - on the hop. The sooner you are able to alert us, the better. 7700 flashes red on our displays, with the abbr. "EMG". If you have time to also bleat at the r/t something like "(callsign) emergency descent, turning 90 left (or right)(or straight ahead)" that is likely to make short term planning easier. Also perhaps TCAS will give an earlier or more accurate warning if the aircraft is deviating in one dimension, rather than two (changing) dimensions.
But, basically, do what you need to do.If you can tell us, great. It would be the mother of all the angels of bad luck to pop a window and then brush wings with someone else on the way down!
Is there a simple "one button push HERE on the SSR squawks 7700" on airline transponders? I'm thinking how time consuming/distracting is it to try and manually reset it. Maybe the quick mayday might be faster?