Wake Vortex in USA

[Keygrip]

Serious question - no "if you don't like **** off home, you will not be missed" answers.

I'm obviously not understanding the USA understanding of wake vortex.

UK recommendations (which are in print) suggest two minutes delay when departing behind a larger aircraft from the same departure point (three minutes from an intersection).

I've never managed to find any recommendations in the FAA publications.

However, on the two recent occassions that I've heard a student be given a take-off clearance immediately after a jet has departed the same point - and said student has declined, citing the desire for (incorrectly) three minutes of seperation for vortex, the controllers have come back and said "You are departing from the same point"- in such a way that they appear to feel that there is NO vortex problem.................yet, on both occassions, a light aircraft on final approach to the same runway for a touch and go was warned about possible vortex problem - despite that aircraft being further away from the vortices.

How can a departing aircraft not be prone to a problem - but a touch and go can??

Also had a warning - some years ago - "Caution wake vortex from the preceding King Air".....but we were both on the taxiway.

[Eva San]

I'm not american and in my country it works just the same way as in England, so I'm just thinking of what could be a reasonable explanation for this difference between a take off and a touch and go.

Maybe the controller considers that when departing behind a heavier traffic from the same intersection, the take off roll will be shorter than the previous one and an earlier turn out would probably help to stay clear of the vortex... Whereas in the touch and go situation, obviously the light one has to land first and then take off , which will use much more runway length and then make it difficult to avoide wake turbulence.
That's all I can think of...

And for your wake vortex on the taxiway, I think it's obviously the vortex from the propellers ... no offense but maybe a tired controller on the position :D

[Keygrip]

Eva - I wondered the same thing about the departing aircraft - but this would require a student pilot (possibly solo) to be starting a turn at only two or three hundred feet a.g.l.

At the latest airfield that I heard this at, noise abatement procedures prohibit this - and any decent flight school training manual would also prevent this kind of operation.

[FWA NATCA]

Keygrip,

The 7110.65 (3-9-6 & 7)that we use in the US is very specific as to the proper application of wake turbelence.

3-9-6
e: NOTE: The pilot may request additional separation; i.e., 2 minutes vs. 4 miles, but should make this request before taxiing onto the runway.

f states: Separate IFR/VFR aircraft taking off behind a heavy jet/B757 departure by 2 minutes, when departing. A pilot can not waive the wake turbelence delay behind a heavy/B757.

3-9-7 a.1: Separate a small aircraft taking off from an intersection on the same runway behind a preceding departing large aircraft by ensuring that the small aircraft does not start takeoff roll until at least 3 minutes after the large aircraft has taken off.

A pilot may waive the 3 minutie delay unless it is a heavy/B757.

b3. basically states that for small aircraft in the pattern must maintain visual separation with the preceding large and be issued a " caution wake turbulence"

Mike
NATCA FWA

[Keygrip]

Mike, thanks for that.

Your message, however, seems geared only to "heavy" classification - any idea what the deal is with say....a PA28 behind a Gulfstream V, a Citation X or a Hawker, for example.

If, as I suspect, they are being classed as 'no vortex threat to the light aircraft departing immediately behind', then why still the warning to another PA28 that is still on a one mile final.

[normally right blank]

We still have the "but caution so and so traffic" if less than ten miles behind. (Hit me, I'm at home).

[FWA NATCA]

keygrip,

A small (PA28) departing behind a large (G-5, LR24, CRJ, etc.)

Full length would only receive a caution wake turbelence.

From an intersection or opposite direction there would be a 3 minute wake turbelence delay that is wavierable by the pilot.

Mike
NATCA FWA

[Keygrip]

Ok - so getting close now Mike :p

As an ATCer - have you any suggestions as to "what would be considered CAUTION"

What would the industry expect of the pilot (student?)??

Take off immediately and go straight ahead - therefore, effectively, ignoring the potential vortex (as ATC would have covered their backs by giving the 'caution' statement)??

Take off immediately and do an early, low level, relatively slow speed, turn into wind - over whatever built up or noise sensitive areas there are - without declaring their intentions not to follow centreline??

Ask, before entering the runway, for the early turn after departure (what if this is refused?)??

Ask, after entering the runway, for the early turn (what if refused?)??

Decline immediate take off until two minutes have elapsed - but run the risk of another jet being cleared to go in the meantime, with yet another two minute delay??

As the only thing a pilot can do about wake vortex is physically avoid it - it seems that ATC just cover their backs with the warning, and then leave the pilot to either risk destroying the aircraft on departure or getting their ears chewed for not taking the immediate take-off clearance or for making an early turn.

Suggestions from anybody - what constitutes "CAUTION"??

[FWA NATCA]

Keygrip,

I don't think that there is a small aircraft out there that can't get airborne prior to the spot where the large aircraft rotated, so the caution wake turbelence is given to ensure that the pilot is aware of the potential of wake turbelence, and to plan their rotation and climb out accordingly.

If a pilot in a small aircraft wants to wait a minute or two, then they should tell ATC prior to going into postion onto the runway.

From what I was trained, in the above situation the pilot will make sure that he gets airborne prior to the spot where the large aircraft rotated, and climb so as to stay above or off to the side of the large aircrafts flight path to avoid any potential wake turbelence.

Mike
NATCA FWA

[Keygrip]

Mike,

Pretty much exactly the answer I expected to the original question (though not necessarily from you, :) ).

Whilst I agree with both points - neither will work on their own.

Of course, every light piston aircraft can rotate before the rotation point of the Hawker/G 5/Lear/Beech 1900 - but I doubt that any one of them can OUTCLIMB the previous high performance aircraft - so the only way out has to be the low/slow/noisy turn off the centreline.

With regards to asking for the delay - that is exactly what caused the original question - I've witnessed it personally at three USA airfields (Naples, Florida; Vero Beach, Florida; Scottsdale, Arizona) and on every occassion (now six times in three years) when students and/or flight test candidates ask for a delay for vortex, ATC have come back at them with a growl, pointed out that they are classed as being at the end of the runway, and have caused substantial delays by letting other HP aircraft before them.

I truly do not see a genuine approach to wake vortex separation on behalf of ATC.

When I used to fly at Manchester (U.K.) it was very common that a light aircraft would be given an intersection departure whilst an airliner was being given a full length "line up and wait, light aircraft departing ahead for wake vortex seperation" clearance.

We still did an early turn when conditions allowed (to let the guy out behind us) - but this was over unpopulated territory that would not write to the airport to complain about noise.

I agree with all your comments, Mike, good text book stuff - but they won't work.

[vector4fun]

Keygrip,

The relevant portion of the U.S. AIM contains the following guidance:


7-3-6. Vortex Avoidance Procedures

a. Under certain conditions, airport traffic controllers apply procedures for separating IFR aircraft. If a pilot accepts a clearance to visually follow a preceding aircraft, the pilot accepts responsibility for separation and wake turbulence avoidance. The controllers will also provide to VFR aircraft, with whom they are in communication and which in the tower's opinion may be adversely affected by wake turbulence from a larger aircraft, the position, altitude and direction of flight of larger aircraft followed by the phrase "CAUTION - WAKE TURBULENCE." After issuing the caution for wake turbulence, the airport traffic controllers generally do not provide additional information to the following aircraft unless the airport traffic controllers know the following aircraft is overtaking the preceding aircraft. WHETHER OR NOT A WARNING OR INFORMATION HAS BEEN GIVEN, HOWEVER, THE PILOT IS EXPECTED TO ADJUST AIRCRAFT OPERATIONS AND FLIGHT PATH AS NECESSARY TO PRECLUDE SERIOUS WAKE ENCOUNTERS. When any doubt exists about maintaining safe separation distances between aircraft during approaches, pilots should ask the control tower for updates on separation distance and aircraft groundspeed.

b. The following vortex avoidance procedures are recommended for the various situations:

1. Landing behind a larger aircraft- same runway. Stay at or above the larger aircraft's final approach flight path-note its touchdown
point-land beyond it.

2. Landing behind a larger aircraft- when parallel runway is closer than 2,500 feet. Consider possible drift to your runway. Stay at or above the larger aircraft's final approach flight path- note its touchdown point.

3. Landing behind a larger aircraft- crossing runway. Cross above the larger aircraft's flight path.

4. Landing behind a departing larger aircraft- same runway. Note the larger aircraft's rotation point- land well prior to rotation point.

5. Landing behind a departing larger aircraft- crossing runway. Note the larger aircraft's rotation point- if past the intersection- continue the approach- land prior to the intersection. If larger aircraft rotates prior to the intersection, avoid flight below the larger aircraft's flight path. Abandon the approach unless a landing is ensured well before reaching the intersection.

6. Departing behind a larger aircraft. Note the larger aircraft's rotation point and rotate prior to the larger aircraft's rotation point. Continue climbing above the larger aircraft's climb path until turning clear of the larger aircraft's wake. Avoid subsequent headings which will cross below and behind a larger aircraft. Be alert for any critical takeoff situation which could lead to a vortex encounter.

7. Intersection takeoffs- same runway. Be alert to adjacent larger aircraft operations, particularly upwind of your runway. If intersection takeoff clearance is received, avoid subsequent heading which will cross below a larger aircraft's path.

8. Departing or landing after a larger aircraft executing a low approach, missed approach, or touch-and-go landing. Because vortices settle and move laterally near the ground, the vortex hazard may exist along the runway and in your flight path after a larger aircraft has executed a low approach, missed approach, or a touch-and-go landing, particular in light quartering wind conditions. You should ensure that an interval of at least 2 minutes has elapsed before your takeoff or landing.

9. En route VFR (thousand-foot altitude plus 500 feet). Avoid flight below and behind a large aircraft's path. If a larger aircraft is observed above on the same track (meeting or overtaking) adjust your position laterally, preferably upwind.


As Mike noted in our 7110.65, there is no provision for a wake turbulence delay when departing from the same point, unless the preceeding aircraft is a Heavy/B757. However, while I'm not familiar with the airports you mentioned, I've never worked or flown at an airport in th U.S., where an early turn, or small offset to the side to avoid wake turbulence by a small aircraft would have been prohibited by noise concerns. All the noise abatement policies I've had to work under only regulate large/turbojet aircraft. Not to say that certain airports don't have strict policies governing small aircraft, but it's uncommon over here. In fact, para 3-9-7 of the .65 contains the following statement:


c. When applying the provision of subpara b:

1. Issue a wake turbulence advisory before clearing the aircraft for takeoff.

2. Do not clear the intersection departure for an immediate takeoff.

3. Issue a clearance to permit the trailing aircraft to deviate from course enough to avoid the flight path of the preceding large departure when applying subpara b1 or b2.

[FWA NATCA]

Keygrip,

The problem with giving all the small aircraft intersection departures and all the large and above full length is that each time that large rolls I have to give the small aircraft a 3 minute wake turbelence delay.

My best option is to take the small aircraft to another runway to avoid the wake turbelence delay, my second option is to take the small aircraft to full length.

I as a controller am not going to hold up large full length departures because a small aircraft requested an intersection departure, and my ground controller had better have the common sense to take you to full length or to another runway, or to warn the small departure that there will be a delay from the intersection.

As to requesting a minute for the wake turbelence to dissapate, that isn't a problem unless you are at a busy airport where they are constantly having to shoot gaps between arrivals. Again the key is to let the controller know soon enough that you want a slight delay. If you are in a line behind large aircraft waiting to depart, you should know right off whether you want a slight delay, so tell the ground controller, or the local controller as soon as possible. I would much rather have you pull off to the side so someone else can depart than to have you hold up the departure stream.

The only time that I get testy with a pilot is when I'm shooting the gap between arrivals and the pilot takes his sweet time taxiing into position and hold, or I've cleared the pilot for takeoff and they just sit there while the traffic on final bears down on them.

Mike
NATCA FWA

[Eva San]

Landing behind a larger aircraft- when parallel runway is closer than2,500 feet. Consider possible drift to your runway. Stay at or above the larger aircraft's final approach flight path- note its touchdown point

My best option is to take the small aircraft to another runway to avoid the wake turbelence delay, my second option is to take the small aircraft to full length.

Do you have the same 2500 feet thing for two departing a/c ?
In my country, if departing from a runway less then 2500 feet away behind a heavier traffic 2 minutes if same "intersection" and 3 min if not.

The other thing I still don't understand is the same as Keygrip. How can you expect a light aircraft to outclimb the preceding if the earlier turn is not available ?

As to requesting a minute for the wake turbelence to dissapate, that isn't a problem unless you are at a busy airport where they are constantly having to shoot gaps between arrivals. Again the key is to let the controller know soon enough that you want a slight delay. If you are in a line behind large aircraft waiting to depart, you should know right off whether you want a slight delay, so tell the ground controller, or the local controller as soon as possible. I would much rather have you pull off to the side so someone else can depart than to have you hold up the departure stream.

Yeah, and what about the traffic overtaking the light one ? If it's heavier traffic, which seems likely in a busy airport, the problem remains the same and one way or another you're gonna have to wait those two minutes sooner or later. I know that time is money, but what is two minutes ?

[FWA NATCA]

EVA,

In the majority of instances I will give the small aircraft a turn away from the path of the larger aircraft. At FWA the majority of our large aircraft depart runway heading and 4000, this allows us to easily turn the smaller aircraft.

The 2500 or less between runways is a problem for those airports that have them, CLE (Cleveland Hopkins) is a prime example.

Mike

[Eva San]

I'm Ok for the early turn.
But in my own experience as a private pilot and controller, I can tell you that with the type of plane I'm used to fly ( 4 seater with 180 hp or even less) it's not really possible.
I'm not supposed to turn below 500 feet which means that I'm not able to do it before the end of the runway ( approx 9000 feet long in my home airport) ... difficult to avoid the wake vorteces in such a case !

Maybe we're just being too cautious, and I guess if you keep on using this method in the states it's because you've never had any accident, which tends to prove that you're right.
Anyway, just please don't be to harsh on a pilot if he's asking for these two minutes or even three, especially if he's not american. For in Europe, the controller has to provide the turbulence separation for departing a/c meaning that the pilot doesn't need to ask for those minutes.

Cheers.

[Keygrip]

Mike - the common intersection departure of which I spoke wasn't a request.

In the earlier days of Manchester International it was a single runway airfield - all the airline stuff was on the North side of the runway, GA was on the Southside.

The single runway - some two miles long - had airline taxiways using intersection A through H covering both ends(full length).

The GA taxiway was a 'loop' that started at intersection C and ended somewhere around E or F.

Without crossing the runway and then joining the airline taxiway (with the subsequent power checks at the hold short line), you had no choice but to go from the intersection - or backtrack.

[FWA NATCA]

Keygrip,

I can understand the problem, if you can't easily get to full length then your only option is an intersection. On the other hand I can understand the long, and I do mean long taxi route problem too. When we are departing Runway 5 (12,000 feet long) it is over 2 miles worth of taxiing to go full length so I rarely see any small aircraft willing to taxi that far so they put up with the wake turbelence delays.

Mike