Track vs. heading - an ATC Q for you pilot-types

[Julian Andrews]

Question for you. Our published noise abatement requires climb to 3000 feet "straight ahead" after dep. After asking why one his aircraft ended up almost 1 nm north of the extended C/L at 3DME, one operator's fleet tech. capt. (modern'ish twin jet) tells me it's because they can't set "track" on the FMS/flight director and hence it defaults to "heading mode". He takes me to task for not publishing a SID (answer: no continuous controlled airspace=no SID) nor publishing a point to which his FMS can take him on the C/L immediately on dep. Sorry-that's no good to me one little bit when Mrs. Angry phones in yet another noise complaint that departing aircraft are "off the flight path, going over her house (sic)". Is "straight ahead 3000 feet before turning" not easy enough to fly"?

Now then, when I learned to fly, I was taught that track and heading are NOT the same thing, a fact that has done me proud in almost 30 years of the ATC game. In order to track the extended C/L in a X-wind and with no "track mode" available on the automatics, why can't flight crews lay off the drift by a simple DR by heading, say, 5 degrees heading into wind, to make good the track required. Too simple? Does this not come down to basic "airmanship"? Or am I just a simple ATCO who doesn't understand company procedures these days and the way modern FMS/flight directors have to work? Your comments would be oh so welcome, pilot-people...

[excrab]

Julian,

I apologise in advance if this gets a bit incoherent due to alchohol intake but here goes.

Obviously I don't know the exact type of aircraft/FMS concerned, but I would have thought that if the FD/FMS is in heading mode it is easy enough to just set the heading bug or enter a command heading to allow for wind, if the aircraft has been instructed to maintain runway centreline to 3 DME. However, if they have got the drift wrong then 3 DME at about 180kts doesn't give much time to correct it and regain track - and on this occasion it would seem to be very wrong as 1 mile after 3 miles along track is about 20 degrees track error ( if I can still work out the 1:60 rule after a bottle of red wine!).

If they consistantly have problems then perhaps they should enter a stored waypoint which could be based ( making a wild stab at your possible location ) on the I-BTS or I-BON DME with runway QDR as the bearing and 3 miles as the distance from the reference waypoint ( which would be the threshold of the reciprocal runway to that used for take-off if you follow me ). Entering this as the first waypoint of a route would take the aircraft to three miles on the runway centreline before turning it whichever way it has to go to join the airway system, and if they took off with the FD selected to FMS NAV mode or the equivalent then they would have steering commands ( either hand flown or with autopilot ) as soon as the wheels were off the ground.

Obviously depends on the limitations of the equipment but would certainly work on the aircraft I fly ( although the 5 degrees on the heading bug for wind would seem the easier option I must admit ).

[The Greaser]

In the US, we were always taught (and teach) that if ATC request 'fly runway heading' that we fly heading and not correct for drift to maintain centreline. If a SID says likewise then we do likewise. Say we enter IMC as we lift off, even if we know the approximate wind, then we are still guessing the drift to maintain centreline if that is what is required.

[Crusty Ol Cap'n]

Obviously not an Airbus as they usually default to runway track after takeoff. In my Boeing days it was quite simple to calculate the drift required to maintain centreline after t/o using the 1 in 60 rule. Sounds like some people are too lazy to bother. They should try to remember that the swept cone for takeoff is actually quite narrow and they really need to stay inside it until 1500'.

[Julian Andrews]

Thanks guys. The company concerned apparently cannot input ad-hoc waypoints unless they are published in the AIP/Jepps/Aerads - I asked and suggested they put one in themselves, after consulting their nav. people and carrying out the necessary risk-assessment etc. It's a thought.

Yes, I take the point about heading - fine if you have a parallel runway situation and want everything departing off both runways to fly the same initial track without fear of confliction. Does anywhere have parallel IFR departure runways, incidentally?

More comments please, with or without the influence of booze. All offers gratefully accepted. How come everyone on this web site is so damned coy about their personal profile? Or am I just naiive enough not to worry about being identified...?

[PPRuNe Radar]

In the UK .....

'Continue straight ahead' = continue on extended runway centreline, making allowance for wind.

'Continue present heading'= continue the heading you are currently on, ignore wind.

[Captain Stable]

"Maintain runway heading" = no correction for drift.
"Climb straight ahead to 3,000" = apply drift.

Yes, he's making a bit of a meal of it. On climbout it is perfectly normal to put a drift correction in manually. You can then set the heading bug on that and fly the bars with the FD in HDG. Put the AP in and it will continue straight ahead.

I can fully understand their company's point about not adding extra waypoints to the FMCS.

I've seen many people do this and the result is generally a nightmare, and dangerous, as Captain Blimp sets it up all wrong. I've seen a point for an 8-mile final placed at the wrong end of the runway, a point for STN AP put in that was 25 miles from EGSS and all sorts of other horrors.

What is generally needed at most airlines (and very few have them) is a navigation officer, whose responsibilities include setting extra nav points in FMCS/GPS/whatever systems they have. If EGxx publishes a new noise departure such as the one above, the captain on his voyage report makes a suggestion for a new nav point to be plotted to facilitate the departure and, in due course, it is done.

However, as I say, it is not exactly hard to fly the procedure correctly without.

[411A]

Hmmm...
Navigation Officer, now there's a novel idea...thought today he/she (to be politically correct) is called the co-pilot. Or, as I suspect, too darn busy pushing buttons on the FMS to account for drift.:rolleyes:

[john_tullamarine]

.. and I would think it quite imprudent, on any obstacle critical departure ... to accept any ATC clearance which differs from the tracking embodied in the escape procedure as published by the ops engs guys and gals ...

In Oz we have a couple of such runways .. and ATC are most obliging ... even when the SID is declined in favour of the escape tracking requirements ..

[Capt Claret]

Any drift allowance is of course only a guess. Without a reference point to track to, as suggested above, one can only guess what the wind is doing with changing altitude and to a lesser degree, horizontal distance from the field.

[Captain Stable]

411A, you miss the point. I'm talking about one officer in the company who has responsibility for the FMCS waypoints, for maintaining a review of computer flight plans, etc. etc.

I am NOT talking about the FO. As my post made quite clear, it is not a good idea to permit crews to insert whatever waypoints they feel like.

Capt, Claret, agreed. But a guess is better than no correction.

john_t, as the original post made clear, this departure has nothing to do with terrain avoidance, but noise abatement. Of course, safety will come first every time, as would any emergency turn in the event of problems.

[john_tullamarine]

then one hopes that the ops eng people have predicated the RTOW schedule on the noise abatement tracking .....

[Captain Stable]

You would hope so, wouldn't you? ;)

[Track]

Quote: hence IT defaults to "heading mode".

Who is flying the plane here :confused: :confused:

On Boeing a/c there is an actual track line, line this up with the extended centerline by using heading and you will fly a perfect runway track. I'm sure every "modernish" jet wil have this feature.

Wonder how this guy will fly a holding pattern....

[steve757]

There may be several reasons for not maintaining runway track, but at the end of the day a bit of awareness and mental Dead reackoning should suffice - the wind on the surface is known and most modern aircraft have some form of wind readout. On Fms aircraft manually flown then keeping the track line on the QDM should again do the trick. Problems may compund when using autopilot/ FMS for departure. The Map may have shifted due to drift in the inertial system, and not all track lines are accurate in the early stage of departure. Selection of autopilot at a few hundred feet should engage roll mode ( boeings) to maintain ground track, which is fine if the track line is accurate and an accurate drift corrected heading is being flown prior to A/P engagement. Even if the track line is accurate, if map shift has occured and LNAV is engaged the aircraft may well deviate significantly to aquire a false offset track. The situation is not helped when published SIDs demand a track and the FMC is programmed to fly a heading.

At the end of the day I suppose there is no substitute for good awareness and airmanship.


The next time Mrs Angry 'phones ask her if she was there before the airport was built.

[Dan Winterland]

In the US, you should fly runway heading after a take off or go around. It's runway track everywhere else.

[Martin Barnes]

What a Great Idea !

GPS-FMS waypoints at 8-9 nm out on the extended
centreline.

At Bristol we could call them ANDREWS and WILSON (for old times sake)

you could even clear the JEA inbounds direct to Wilson to report established then they would not complain about you ****ty vectoring (joke)