How to avoid wake turbulence?

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rookie1255

Pre-takeoff checklist
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rookie1255
So I know that you take off before a jet or land after their landing point. How about if you're holding short waiting for a landing jet before takeoff. Would you try to take off before their landing point or would this take you right through the wake turbulence?

The alternative would be rotating after their landing point. This would have the airplane accelerating though the wake on the ground but then avoiding it on the rotation.
 
Another option not mentioned.... waiting....

If the pattern and/or departure area isn't crowded, and Tower is cool with it, just ask for a delay to allow the wake turbulence to move off the runway.


Back to your question, AC 90-23G, Aircraft Wake Turbulence, will provide guidance on the subject.
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We were holding at SKF yesterday and a C-5 was doing touch n gos. Tower tried to position and hold I mean line up and wait us :D, and as me and my wingman looked at each other and waved our nuggets with the international signal for "NFW José", tower quickly cancelled the instruction. We waited.

We have our expanded wake separation criteria to observe, above and beyond civil requirements and/or practices. Most of the time it mimics civil regs, but in many other respects it is more restrictive than civil part 91 (VFR definitions, alternate wx requirements et al for instance). Usually we're pretty go-oriented and feed the fight on pointy nose fuel-deficient jets, but taking off behind dash Heavy airplanes is one exception to that mantra :D
 
AggieMike88 said:
@hindsight2020 .... what aircraft were you in?
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96d3012e43ef0791a20c42171ab456e2.jpg
 
rookie1255 said:
So I know that you take off before a jet or land after their landing point. How about if you're holding short waiting for a landing jet before takeoff. Would you try to take off before their landing point or would this take you right through the wake turbulence?

The alternative would be rotating after their landing point. This would have the airplane accelerating though the wake on the ground but then avoiding it on the rotation.
Click to expand...

You takeoff before the jet and land after the jet because you are trying to find a flight path where the jet's wings are no longer producing lift. Landing past the jet, allows the jet to be firmly on the ground and the wings to stop producing lift by the point where you land. Taking off before the jet again has you in the air before the jet has left the ground and the wings have started producing lift; since the jet's climb performance is likely greater than your own, you are almost certainly going to fly through their wake turbulence if the winds are calm and you maintain runway heading but the idea is to get airborne and to a safe altitude and airspeed before encountering the turbulence as well as giving you options to deviate from runway heading/flight path to the upwind side to avoid the turbulence.

So in answer to your question, where do you take off with a jet on landing? Your best bet is probably taking off beyond their point of touch down. There will be no wake turbulence past this point to worry about on climb out. You may experience some wake "turbulence" before rotation and you should anticipate that but it should be largely manageable because you are at a slower speed and are firmly planted on the ground yourself with positive steering control via the brakes/steerable gear.

Trying to take off before the point of landing is particularly dangerous as you will need to get off the ground quite rapidly and you will encounter their wake turbulence once airborn at a lower airspeed and quite close to the ground. It's always easier to length a takeoff run than it is to shorten one.

Large jets practicing TNGs as described by @hindsight2020 are rather rare encounter but do happen. TNG's present a particular challenge because the window in which the large jet is not producing lift is a very narrow window and because the jet is likely to have plenty of speed, they are likely to have a steeper climb gradient that you wont be able to match or get to a safe altitude with. For this reason with TNG's, your best bet is to wait for the wake turbulence to dissipate which the FAA says takes about 3 minutes.
 
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When I was checking out at ICT, I was taught to jig slightly upwind in any crosswind component instead of tracking the extended runway centerline. We did quite a few touch and goes sandwiched around heavy departures with no wake encounters, observing all the other usual wake precautions.

When approaching busy terminals in trail of heavies, I always ask for as much separation in trail as I can get. (Of course, a 737 leaves me in the dust anyway.) Better yet, some airports, like BWI, have a whole separate runway for GA traffic. That's the best.

Sometimes Tower can help. At GSO, i got cleared for an intersection takeoff during the am rush, cutting ahead of a whole string of airliners. Nyah, nyah! But seriously, It was nice to not get stuck waiting for wake dissipation, and I was out of everyone's hair quickly.
 
I did my primary training at CYOW (a busy mixed-use airport), so "Caution, wake turbulence from departed..." was a normal part of clearances. The rules are simple:
  1. Count 120 steamboats before you accept a takeoff clearance from a runway where a heavy has taken off or flown across low. If ATC clears you before then, decline.
  2. Stay above the heavies. If there's one ahead of you, it must be a big runway, so land longer (after its touchdown point) and take off shorter (before its lift-off point). That 8,000 ft runway is long enough for your little plane to do 5 consecutive touch and goes—no need to put the wheels down right in the TDZ.
  3. Do a steeper approach. Jetliners usually need a 3° glidepath. Our little single-engine piston trainers can handle 5–6° without breaking a sweat, so if you're sharing an approach path with heavies throw the "stabilised approach" stuff out the window (you're not a jet), stay high as long as you can, then cut power, drop flaps, and drop it in long.
Actually, one more rule: treat every helicopter, no matter how small, as if it were a 747. Those rotors make a lot of turbulence.
 
apr911 said:
Large jets practicing TNGs as described by @hindsight2020 are rather rare encounter but do happen.
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Couple years ago I was OIC at the USMC Expeditionary Airfield (EAF) at 29 Palms, CA. Every once in a while we’d get AZ C-17s that would come out for “austere site” codes...
But if the wind was calm enough we’d have them do normal T&Gs then switch it up so we could try and mitigate the airfield matting shifting too far in one direction.

Total non-sequitur...
 
David Megginson said:
I did my primary training at CYOW (a busy mixed-use airport), so "Caution, wake turbulence from departed..." was a normal part of clearances. The rules are simple:
  1. Count 120 steamboats before you accept a takeoff clearance from a runway where a heavy has taken off or flown across low. If ATC clears you before then, decline.
  2. Stay above the heavies. If there's one ahead of you, it must be a big runway, so land longer (after its touchdown point) and take off shorter (before its lift-off point). That 8,000 ft runway is long enough for your little plane to do 5 consecutive touch and goes—no need to put the wheels down right in the TDZ.
  3. Do a steeper approach. Jetliners usually need a 3° glidepath. Our little single-engine piston trainers can handle 5–6° without breaking a sweat, so if you're sharing an approach path with heavies throw the "stabilised approach" stuff out the window (you're not a jet), stay high as long as you can, then cut power, drop flaps, and drop it in long.
Actually, one more rule: treat every helicopter, no matter how small, as if it were a 747. Those rotors make a lot of turbulence.
Click to expand...
Dave summed it up well here.
I learned to wait 2 minutes before taking the runway after a departing or landing heavier craft.
Would also add if you are around a heavier craft in a small GA craft you might want to avoid being anywhere close to its hind-end at any time.
 
FORANE said:
Dave summed it up well here.
I learned to wait 2 minutes before taking the runway after a departing or landing heavier craft.
Would also add if you are around a heavier craft in a small GA craft you might want to avoid being anywhere close to its hind-end at any time.
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Yes, that's an important point at mixed-use airports. If you're taxiing behind a Boeing or Airbus (or even a small jet somewhere like Teterboro), allow lots of extra room so you don't end up splattered against the airport fence from jet blast if they accidentally advance the throttle too much.
 
Its better to understand where and when wake turbulence occurs in order to understand how to avoid it.

The 2 minute count can be a bit much. Its a great general rule of thumb sure and its one that I recommend to students but if you decline every clearance that has you taking off 2 minutes or less behind a heavy takeoff or landing, at some busier airports, you'll never get out. 2 mins can also be less than the FAA recommendations of up to 3 minutes which is itself incomplete in that wake turbulence can linger longer under certain conditions.

I've spent 30 minutes on the ground at KSAT once just waiting for the 60 second window that tower finally gave me between two heavy's and KSAT isnt even all that busy (and was even less busy 7 years ago when I had this encounter). I got a line-up-and-wait as soon as the first heavy crossed the threshold and a cleared for take-off, no delay, 737-heavy on short final (think it was a 3NM final but not sure just how far it was since it was so long ago, just remember thinking how tight of a slot it was and how the plane was right on my tail) as soon as the first heavy cleared onto the taxiway.

Also note that while jets typically follow the ILS glideslope in, which is 2.5 to 3.5 degrees in a lot of places (but can be more), they are perfectly capable of steeper approaches. London City airport has a 5.5 degree glide slope so it'd be false to assume the jets are always going to be on a 3 degree glideslope, especially when doing visual approaches; I followed a jet in the other day on a visual approach that had to be close to 4 degrees given the 650fpm descent rate I needed at 90kts to keep above its path. It also would be a bad practice to get in the habit of as it limits your options in instrument conditions as full scale deflection on the glide slope occurs at 1.4 degrees.

Lastly, stable approach criteria has little to do with the angle of descent. Stable approach criteria merely means that your approach is consistent; you are at the desired airspeed, trimmed out and descending at the desired speed without requiring major adjustments of elevator, power or other configurations... You are in a "stable" configuration that can be continuously flown down to the runway. You can have and meet stable approach criteria on a 5 degree glide slope but the steeper the glide slope the more work is required to maintain it and the easier it becomes for the approach to become unstable.

Good advice on the helicopter rotor wash/vortices... They can be worse than any heavy.
Good advice on the taxi/following distance of a heavy. That can impact any plane but in a STOL Tailwheel you can get enough of a blast to actually fly (momentarily at least) followed by an abrupt no-lift crash.
 
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John Bussard said:
Couple years ago I was OIC at the USMC Expeditionary Airfield (EAF) at 29 Palms, CA. Every once in a while we’d get AZ C-17s that would come out for “austere site” codes...
But if the wind was calm enough we’d have them do normal T&Gs then switch it up so we could try and mitigate the airfield matting shifting too far in one direction.

Total non-sequitur...
Click to expand...

How does that work there? Where you stationed there or just there for an exercise?
 
David Megginson said:
I did my primary training at CYOW (a busy mixed-use airport), so "Caution, wake turbulence from departed..." was a normal part of clearances. The rules are simple:
  1. Count 120 steamboats before you accept a takeoff clearance from a runway where a heavy has taken off or flown across low. If ATC clears you before then, decline.
  2. Stay above the heavies. If there's one ahead of you, it must be a big runway, so land longer (after its touchdown point) and take off shorter (before its lift-off point). That 8,000 ft runway is long enough for your little plane to do 5 consecutive touch and goes—no need to put the wheels down right in the TDZ.
  3. Do a steeper approach. Jetliners usually need a 3° glidepath. Our little single-engine piston trainers can handle 5–6° without breaking a sweat, so if you're sharing an approach path with heavies throw the "stabilised approach" stuff out the window (you're not a jet), stay high as long as you can, then cut power, drop flaps, and drop it in long.
Actually, one more rule: treat every helicopter, no matter how small, as if it were a 747. Those rotors make a lot of turbulence.
Click to expand...

Oh Yeah. It ain’t just rotor wash. They make a wake. Vortices. I got in one of them just before flaring in a C150 once. My pulse is going up right now just remembering it
 
I operated a 170, 172, and my Navion out of IAD. I never had an issue with wake turbulance while holding, mostly because I was 1000 away from the flight path. Airliners don't touch down before the fixed distance markers (GS intersection with the runway) usually.

A bigger issue you need to watch with ground ops is jet blast. My wife was heading down taxiway Z at IAD (well it was probably W2 back then before the FAA decided to screw up the taxiway designators). A FedEx jet on the air cargo ramp ran up its engines and skittered her toward the edge of the taxiway.
 
Taxi past their touchdown point and take off from there assuming you still have enough runway. Since you said we're waiting for a jet, I assume this is a long runway.
 
hindsight2020 said:
We were holding at SKF yesterday and a C-5 was doing touch n gos. Tower tried to position and hold I mean line up and wait us :D, and as me and my wingman looked at each other and waved our nuggets with the international signal for "NFW José", tower quickly cancelled the instruction. We waited.

We have our expanded wake separation criteria to observe, above and beyond civil requirements and/or practices. Most of the time it mimics civil regs, but in many other respects it is more restrictive than civil part 91 (VFR definitions, alternate wx requirements et al for instance). Usually we're pretty go-oriented and feed the fight on pointy nose fuel-deficient jets, but taking off behind dash Heavy airplanes is one exception to that mantra :D
Click to expand...

Was the tower controller trying to save time by getting you on to hold and waiting the two minutes, rather than waiting the 2 minutes THEN clearing you for take off from the taxiway? I ask because sometimes its the only way we can get people out. That precious time spent taxiing onto the runway, runway and then rolling is a lot with some aircraft.
 
That precious time spent taxiing onto the runway, runway and then rolling is a lot with some aircraft.
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It's got squat to do with "aircraft" but some pilots. I was up in the IAD tower one day when the controller cleared someone to takeoff and turned back a minute later to find them still sitting in position on the runway. C'mon guys, you're not "ready" unless all you have to do is push the knobs forward to go.
 
Although I would agree with you, I meant "aircraft" because some (such as the A-10 and was in response to a military pilot) require a run up on the runway to develop fan speed before brake release. They can't accomplish this until they get on the runway. In the summer in high density altitude it can take up to a minute.
 
Timbeck2 said:
Although I would agree with you, I meant "aircraft" because some (such as the A-10 and was in response to a military pilot) require a run up on the runway to develop fan speed before brake release. They can't accomplish this until they get on the runway. In the summer in high density altitude it can take up to a minute.
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I let tower use visual sep once with an H-46 on 3 mile GCA vs a flight of F-18s departing. Didn’t go well. F-18s took forever and the H-46 reported looking down thru his chin bubble and seeing afterburners. Not the way visual is supposed to be applied. Local got suspended and I got a stern talking to. :(
 
luvflyin said:
How does that work there? Where you stationed there or just there for an exercise?
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Was stationed there, have flown out of there for exercises as well though...
It’s only “expeditionary” in the sense that it’s what it would look like IF we threw one down for real. This one (KNXP) has been installed for a couple decades now...
 
Timbeck2 said:
Although I would agree with you, I meant "aircraft" because some (such as the A-10 and was in response to a military pilot) require a run up on the runway to develop fan speed before brake release. They can't accomplish this until they get on the runway. In the summer in high density altitude it can take up to a minute.
Click to expand...

That was a thing with F4’s we worked. Don’t know if it was “fan speed,” but there were some things they had to do on the runway. Whether it was Squadron, Group, Wing, Service rules or just an F4 thing I dunno. But ya had to plan for space to accommodate it.
 
John Bussard said:
Was stationed there, have flown out of there for exercises as well though...
It’s only “expeditionary” in the sense that it’s what it would look like IF we threw one down for real. This one (KNXP) has been installed for a couple decades now...
Click to expand...

Oh. When you said OIC, I figured you to be part of the ground operation like the OIC of a MATCU, not a pilot. I was stationed there many years ago when the ‘airport’ was just used a couple weeks a year. I think it was part of that big thing they do out of Nellis every year. It was years later it got Charted with a Control Zone and a Navy ‘Nxx’ identifier, NXP. Before that it was 4TP. Runway was a mishmash of PSP and other kinds of steel runway. Only Harriers and Helos used it when it was operating
 
Velocity173 said:
I let tower use visual sep once with an H-46 on 3 mile GCA vs a flight of F-18s departing. Didn’t go well. F-18s took forever and the H-46 reported looking down thru his chin bubble and seeing afterburners. Not the way visual is supposed to be applied. Local got suspended and I got a stern talking to. :(
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If ya was at sea they’d a thrown you off the stern. That’s if they didn’t keel haul your scurvy dog azz first.:D
 
It doesn't need to be heavy aircraft. A couple of Cessna 206 floatplanes took off from Bedwell Harbor..................the second got in the wake of the first and rotated into the water upside down.
 
Yesterday I just waited 3 minutes.
 
luvflyin said:
Oh. When you said OIC, I figured you to be part of the ground operation like the OIC of a MATCU, not a pilot. I was stationed there many years ago when the ‘airport’ was just used a couple weeks a year.
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Both. The MWSS takes aviators so I had flown there, then OIC for a couple years before returning to cockpit. It’s scheduled daily by PPR, but operating most days of the year. Sees visiting units during most Integrated Training Exercises (ITX) and day to day traffic doing local training as well as VIP ops...
 
luvflyin said:
Oh. When you said OIC, I figured you to be part of the ground operation like the OIC of a MATCU, not a pilot. I was stationed there many years ago when the ‘airport’ was just used a couple weeks a year. I think it was part of that big thing they do out of Nellis every year. It was years later it got Charted with a Control Zone and a Navy ‘Nxx’ identifier, NXP. Before that it was 4TP. Runway was a mishmash of PSP and other kinds of steel runway. Only Harriers and Helos used it when it was operating
Click to expand...
Were you there during AGSD days or prior? Runway now all AM2, it’s on a 5 year cycle, so frequent ops to incrementally remove/repair matting when it comes due. The CDSA is funny when you consider it sits within a Restricted Area...
 
John Bussard said:
Were you there during AGSD days or prior? Runway now all AM2, it’s on a 5 year cycle, so frequent ops to incrementally remove/repair matting when it comes due. The CDSA is funny when you consider it sits within a Restricted Area...
Click to expand...

I was there 73-74. What is AGSD?
 
Timbeck2 said:
Was the tower controller trying to save time by getting you on to hold and waiting the two minutes, rather than waiting the 2 minutes THEN clearing you for take off from the taxiway? I ask because sometimes its the only way we can get people out. That precious time spent taxiing onto the runway, runway and then rolling is a lot with some aircraft.
Click to expand...

I'll never know his intentions, but I suspect the former. We don't take long on the runway from a systems perspective. Our limitations pilot-induced, aka we're training our chickens here, so the students are gonna bone up the formation takeoff run up every now and... well pretty much every time LOL.

It was hilarious watching that C-5 pull closed. It was like a WWII hangar got loose and took a lap around the airport. No way we were gonna take min sep T/O roll behind that thing though. My rickety rocket needs at least 250 knots before it starts behaving like a bona fide fully assembled aircraft. Anything slower than that and this is what I'm essentially driving
upload_2019-6-11_12-36-38.png
 
John Bussard said:
Couple years ago I was OIC at the USMC Expeditionary Airfield (EAF) at 29 Palms, CA. Every once in a while we’d get AZ C-17s that would come out for “austere site” codes...
But if the wind was calm enough we’d have them do normal T&Gs then switch it up so we could try and mitigate the airfield matting shifting too far in one direction.

Total non-sequitur...
Click to expand...


I HATE Camp Wilson with a passion. Like, really hate that place.
 
Unit74 said:
I HATE Camp Wilson with a passion. Like, really hate that place.
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When you consider they had to concrete the K-Spans to make Wilson as livable as Anbar Province...

I was at NAS Fallon a couple years later and everyone thought I’d lost it, raving about how lush and verdant it was in NEVADA...
 
John Bussard said:
When you consider they had to concrete the K-Spans to make Wilson as livable as Anbar Province...

I was at NAS Fallon a couple years later and everyone thought I’d lost it, raving about how lush and verdant it was in NEVADA...
Click to expand...

Psssshh... that’s soft.

I stayed in the A frames. Seriously. Had an 18 drop a 500 100m from our LP/OP out by Lavic Lake once during a CAX. Shut training down for two days, all frozen in place. Cpl Glass was never the same. Kid you now, he was taking a dump behind a rock pile and got peppered with rocks and dirt. Ran back with TP streamers in trail and his drawers half pulled up.
 
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