busy @ stansted airport
 

hello,

I was watching ladnings one late evening and noticed that it was about 30 seconds between a liftoff of a B757 leaving the runway and a B737 landing.. what is the minimum separation or is it just as long as the runway is clear?

thanks,
pitottube

Busy?? At Emmerdale?? Don't give them ideas, please!!

What kind of answer is that????????:mad:

Not an ATCO myself but I believe it's something in the region of either 2000 ft (metres?) airborne or 2500 ft (metres?) down the runway. This is information that I read somewhere a ver long time ago so no doubt I will be corrected.

I believe its a minimum of 2000m, the airport has to have SRG approval, and strict criteria apply to it's use, i.e by day only and a minimum visibility.
An excellent way of managing traffic more efficiantly, now, if we could only do it when they are 700m apart........... :E

Who wasted those 29 seconds then?

Once the departure is airborne, the lander can be cleared to land. Doesn't matter if he's 20 feet or 20 miles away. Of course this in in good weather. In low vis much stricter requirements apply of course.
The thing you always have to take into account is a possible go-around. You don't want a 737 going around from a hight of 30 feet while a turbo prop airborne less than a mile a head of it. No matter what the weather is.

C

You can actually have the departing and landing on the runway at the same time providing that it is a jolly nice day and they are far enough apart......... after the departing XXX cleared to land....works a treat....mostly

There are two different issues being discussed here. At ANY airport, an approaching aircraft can be cleared to land as soon as a departing aircraft is airborne, and that means the lander can be floating over the numbers as the departure gets airborne. Not a problem as long as you tee up the pilots - did it all the time in my old location.
At SOME airports (LL, KK, CC) in the UK, and maybe SS?, "land after the departing" can be given provided the departure is a certain distance along the runway even of not airborne.
In summary, yup, it was a wasted 29 seconds.

landing clearances
 

Thirty seconds is a long time. Let's say the inbound aircraft are flying 2.5 miles a minute on final with 5 mile gaps between. Each landing aircraft is taking 45 seconds to roll out and vacate the runway. If the departing B757 takes 45 seconds to take off, then you're left with that wasted 30 seconds. It only needs a slower than expected take-off, a missed exit on landing, or a faster than expected final approach speed to eat into that wasted time.

On a nice day with a dry runway, ATC can use conditional clearances in order to avoid clearing an aircraft to land while it's floating at 2ft over the TDZ. It also makes us look like we're planning ahead, which of course, we are.

The "land after the departing" procedure makes provision for two aircraft to use the runway simultaneously. It can be employed when the controller anticipates that the departure will be at least 2500m along the runway when the arrival crosses the threshold. On runway 23 at EGSS, this is somewhere between links L and K.

The procedure can also be used when the controller anticipates that the departure will be airborne by the time it reaches 2000m. The distance reduces further for smaller types.

Responsibility for separation rests with the controller in the above instance. (S)he knows that the distances and speeds involved will ensure that the departing aircraft WILL clear the runway one way or the other.

Conditional landing clearances can also be issued to aircraft following another lander. In this case, responsibility for separation from the vacating aircraft ahead rests with the pilot, as only he knows how good his brakes are.

Is the fact that one of the aircraft was a B757 of any relevance? Obviously, the wing tip vortices of a departing aircraft take effect too far along the runway to affect arrivals, except in the case of a missed approach. However pilots occasionally complain that they have felt the jet blast of a recently departed heavy aircraft, particularly tail-engined MD11-type types.

It's interesting to note just how many different interpretations of such a common occurrence there seem to be. I wonder if this confusion exists in any other areas?

And for the record, I'd rather be at Emmerdale than Eastenders any day!