How Do Airline Pilots Do This??

[Easy226]

I was listening to a london frequency earlier and you could hear the controller descend a plane to a certain level xxx miles before a beacon, in this case i think it was 50 before Bovingdon. How do pilots program the FMC. to descend to that level at that exact point, just curious.
Also, where are the Daventry and Cotswold sector contollers situated???

[5milesbaby]

A VERY basic respose is that a/c can pinpiont their position almost exactly using lat and long positioning. Given such an instruction means the FMS calculates where the restriction is lat/long wise, and bases descent on that. These days comercial a/c don't really have to tune into beacons for navigational purposes. The older meathod is using a Vhf Omnidirectional Radial (VOR) with associated Distance Measuring Equipment (DME), whereby the onboard equipment 'moves' the VOR to the distance required, in this case, 50nm closer. How this is done a pilot will better explain, but there are buttons on the FMS which you just hit and put in the required distance.

The Daventry sector controllers (FL200+) are based at Swanwick (Nerc) the airspace FL195- being Cowly/welin airspace based at LTCC, West Drayton. By Cotswold I think you mean Bristol/Brecon/Strumble controllers who are also at Swanwick.

[FlapsOne]

The FMC knows where the aircraft is and where the beacon is.

Simply enter 'BNN - (minus) 50' and qualify that with the FL restriction and the FMC will command a descent to be at that FL 50nm before BNN.

Many FMCs get it spot on, but sadly others have to be monitored very closely.

[mattpilot]

... or you could use your head :) Get rid of the hi-tech stuff and get back to the old days of flying :D

If you know your aircraft pretty well and are paying attention to your current situation, you will know basic data. Like, nm/min. , or standard (most economical) Rate of descent.

example:
Given: standard descent: 2000fpm
5nm/minute

Say you are at FL320 and need to descend to FL200. You are 50miles out. ATC tells you to be at assigned flight level at the fix, and not sooner or later.
Some quick thinking tells you that you need 6 minutes to descent at standard rate and its gonna take you 10 minutes to get to the fix. So what do you do? You wait 4 minutes and then descend at standard rate.

I bet this got some grey brain cells all worked up :D

[OzExpat]

How's this for even easier... in the aeroplane I fly, FL320 is out of the question but a 12,000 feet height loss isn't difficult to work out. I just use a standard 3 times height (in thousands of feet) for TOPD. Thus, in my own case, from FL260 to FL140, is the same 12,000 feet.

12,000 / 1000 = 12
Standard Profile : 3 x 12 = 36NM for descent.
I'm currently 50NM from the fix, so I wait until 36NM from it and then commence descent at 4NM per minute, at 1500 FPM. If you want to work that out the hard way...

12,000 / 1500 = 9 minutes.
9 x 4 = 36NM.

The simpler way works for me every time, all without the use of a FMC. I don't have one of those anyway and I'm a bit of a lazy sod when it comes to doing maths. The "3 times" system suits me almost all the way down to the ground! :)

[mikef]

With the UNS system I've been using of late when an arrival clearance is issued the database has the STAR's in it as well as any height requirements. Selecting the appropriate STAR builds the flight plan. The VNAV profile is "built" from that and it's just a matter of me monitoring the digital profile readout on the EADI as we descend.

If ATC issue you a height restriction it is just a matter of defining the point and inputting the height at that point into the computer. Same as before, the profile is built and you command the descent and monitor to make sure you are on the correct side of the desired point.

These days it seems you can't fly with your index finger!! :)

[Earthmover]

Another way is to use the 3 X method, but for V/S use half your groundspeed x 10 plus 10% - works a treat.

[Easy226]

Thanks for the replies everyone, always wanted to know how you did that. WHich aircraft do you have to monitor very closely then. Why dont all planes have the same accuracy??!

[BOING]

Keen young co-pilot asks captain how he plans his descent . Reply, "Start down 100 miles out eastbound and 90 miles out westbound, Sonny".

[Offset]

Or, of course, if it's 0630 and the end of a Larnaca, you just go down straight away because all the other options involve too much brain power...

[WX Man]

So what would cause your FMC to spit a conditional clearance back saying "no way mate!"? We as student ATCOs get taught that anything beyond about 3000 fpm is to be avoided as a ROD for pax comfort.

[mattpilot]

I dont know about that... :)

I was listening to JFK tower (and its tracon), and the controller asked him if he could increase his descend rate. The planes' pilot replied, "We are alrady doing 5000fpm!"