Approach separation

[lederhosen]

The TCAS thread on the technical forum has reminded me of another practical use of the display, assessing the distance you are behind the traffic in front on final. Once established I tend to set the range to five miles and if the guy in front appears on the display it is a reminder to think about how far he is ahead. Obviously depends on the airfield and the expected separation.

If we are asked to slow down, for example to allow a quick departure in front, it bugs me when the guy behind does not react until asked by ATC and then I am put under pressure to expedite clearing the runway. This happens so often I am beginning to wonder if I am doing something wrong. Do you want us all to keep up maximum speed until told to slow down, or is it better to use common sense and not get to within three miles and then ask sarcastic questions about what kind of aircraft is ahead.

[GunkyTom]

If ATC don't give you a speed restriction, then they are happy with the spacing ahead/behind you. We know spacing erodes and take that into consideration. As long as it doesn't erode below what is the norm for your unit then from an ATC pov, no problem. If it does, either we haven't applied the speed control or spacing correctly or the pilot hasn't complied with an instruction. If in doubt, ask

[lederhosen]

In short you do not want us to use initiative and slow down if we are catching up the guy in front. Fine by me it is a lot easier.

[Blockla]

The spacing on approach varies; runway configurations, wake spacing, noise abatement, types of approaches and missed approach paths etc.

Keeping a concept of 5 miles may work at some airports but at many others this is a 'fat gap'. The controllers may be banking on the current gap reducing, I know I certainly did when I worked on Approach. Helping yourself to a slow down to help us out may in fact make it more difficult for us. ie force us to slow the one behind you when everything was fine until you reduced your speed and then asking you to get off the runway quickly.

However, you are able to fly your own speed once cleared for the approach unless a speed restriction has been applied; so technically you're doing nothing wrong.

Rather than slowing without reference to ATC, why don't you ask if they would like you to start slowing too; or perhaps ask what gap they are looking for, it might be 3 miles or 2.5 miles?

Always better if you can to make a phone call to the relevant control facility if it's a constant location where you are having issues.

[lederhosen]

I very carefully said think about how far ahead he is rather than help myself to a slowdown! The TCAS range of 5 miles just happens to be the most convenient on my aircraft as the next range up of 10 miles makes the distances very difficult to estimate.

You guys can be working with a pretty blunt instrument as well. When cleared for the approach our SOP is generally to be flaps five at glide slope intercept and to further configure at 2000' agl, to be stable by 1000'. As our 737 NGs can be considerably slower than the classics (due to crossover speeds), at flaps five there can be up to a third of a mile difference per minute in approach speed if we just fly to SOP. I do not believe you know our landing weight and therefore VREF just on my type alone can differ by 20 knots.

If the guy behind starts catching up we are normally told to maintain 160 to some point which is convenient for you but confusing for my new co-pilots. In the classic it is below flaps 5 speed of 170 so they sometimes ask if they should lower the gear so they can get flaps 15, which is quite the opposite of what you want, which is to maintain separation from the aircraft behind. If the speed reduction point is too close in, (say 4 miles) then we risk not being stable.

I am not having a whinge at ATC, if anything my complaint is about fellow pilots blasting in oblivious to what the guy in front is doing. I do in fact inform ATC if we think a reduction would be helpful. I am not sure ringing up ATC to complain about what other pilots are doing is going to help much. In my opinion the wrong crew gets punished. The purpose of starting a discussion on ATC Issues is to discuss this with ATC professionals. I regularly attend runway safety meetings on behalf of my company and find such exchange of ideas useful.

[ADIS5000]

Leder,

If ATC are doing their thing correctly(!), if there is no speed control instruction given to you then fly the speed you want to fly. If you are given a speed restriction ie 160 kts until 4 miles then you must fly at that speed or else you will erode the spacing required by ATC.

If you are constantly being asked to expedite clearing the runway then this sounds to me like an ATC problem (unless you are one of those companies who are always very slow to vacate!). If they slow you down so much that they always have to ask you to expedite, then they should have slowed the one behind you down too. Also, although you do have ultimate responsibility for the safety of your aircraft and must ask if you think that you don't have the required spacing for either separation or wake turbulence don't try to 'second guess' what spacing ATC are trying to achieve. The gaps at any airport can vary significantly from minute to minute depending on the number of arrivals, departures, runway inspections etc etc. As an Approach Controller having 3 or 4 pilots in a row all trying to help out by adjusting the spacing to what they think ATC want would be a nightmare!!

This is just my personal opinion, I'm sure others may take a different view!

Regards, ADIS