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RJ Wake Clearance for Piston Single

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An office with a view
Dec 3, 2001
Please let me know if you think I was wisely cautious or overly paranoid today:

In a 172 with a student we were told position and hold. (There was a CRJ already in position getting ready to go.) As the jet rolled we pulled into position. Just as the jet rotated, about halfway down the 6,500' runway we were cleared for "immediate takeoff, fly runway heading, traffic on 2.5 mile final." Having healthy respect for vortices even from small jets, (I was rolled instantly to a 70 degree bank by a departing F-16's vortex in a C-152 several years ago), I keyed up and quickly said, "we'll need an immediate turn out for wake clearance or we can't go."

Controller responded with an incredulous, "for a REGIONAL jet?"


"Ok, left turn approved."

"Ok, thanks that should keep us clear."

(slight pause)


We had only rolled a few feet so we still had room to turn into the mouth of the taxiway at the approach end. But three other planes in line blocked the hold short line and we had to stay slightly to runway side of it.

The controller was pleasant and didn't seem upset when subsequently clearing us to go again after the landing traffic clear, but then again wasn't apologetic for putting us in a tight box I felt was unsafe.



AIM 7-3-8
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.
3.3.b.A 3 minute interval will be provided when a SMALL aircraft will take off:
1. From an intersection on the same runway (same or opposite direction) behind a a departing LARGE aircraft,
2. In the opposite direction on the same runway behind a large aircraft takeoff or low/missed approach.
d. Pilots may request additional separation, ie, 2 minutes instead of 4 or 5 miles for wake turbulence avoidance. This request should be made as soon as possible on ground control and at least before taxiing onto the runway.

From what I can see, you were partially at fault for not alerting the controller about you requirements for wake turbulence separation prior to taxiing onto the runway. I am sure the controller was a bit annoyed over that. A 172 will easily rotate prior to a CRJ and you could have tracked upwind of the CRJs climbout. No biggy...simply technique. What I think you did very well was exercise your PIC authority. You didn't think it was safe so you declined the controller's suggestion. A lesser pilot would have been pressured into a takeoff they didn't feel safe with. Good decision.
Agreed. Always better safe than sorry. Could've sidestepped upwind a bit instead of asking for the turn. Should've asked before rolling on to the rwy. Excellent job not blindly following the controller's opinion. If it doesn't feel right, it probably isn't.

Has anyone out there ever had a vortex encounter with small jets? How about a little larger (727, A320, etc.)? We get this a lot at our airport and I've always been curious.
The winglets on the CRJ lessen the effects of the wake vortices, don't they? (To some extent). I would have gone in that situation... I don't think the RJ's wake vortices are powerful enough to do any damage.
A 747-400 also has winglets. Doesn't mean the wake will be any less. Be conservative, just because a plane has winglets don't be fooled that the wake will be any less. It may, it may not. Treat them all the same.

Fly safe!
You can definitely get rocked behind an RJ in a light aircraft. I've been rocked in a 23,500# jet following a 27,000# jet. Don't let anyone tell you differently.

Use technique where you can, and delay when you can't.

Good job not allowing yourself (and your student) into being bullied into a situation you felt was unsafe.

Another situation I encountered happened in a Piper Arrow, taxiing to the active runway. Just prior to passing behind a B767 (who was preparing to cross the active), the controller cleared him to "cross without delay". I was very nearly flipped over (and I mean one of my mains was off the ground, with full aileron). When the moment passed, and I told the controller what happened, he said, rather snidely, "YOu taxi at your own discretion", which really pi$$sed me off, since I had almost been killed.

I told him that I taxiied as cleared, and that I am not a mind reader, but if he wanted me to call him and discuss it further, I would be happy to. I hope that idiot learned something that day, I know this idiot did.
Sometimes the wake from the SAME type can give you a start, and the wake from an RJ can shake you up in a light aircraft. I would have done exactly as you did. For some reason, people, including controllers, seem to think that because RJ's are quiet and small, that they don't have any wake behind them. This is not correct. The winglets do help a bit, but you are still getting behind a 50,000 lb aircraft.

I think you did the right thing.
Years ago I was packing a parachute in a downstairs loft. I heard some commotion, and a student jumper entered the loft holding a deployed reserve. His main parachute was gone. I recognized the rig; it was a student rental rig, and I had packed the main. I was immediately interested in the malfunction, and why the student had cut away.

I soon learned the student didn't need to cut away. I felt a need for vindication, as I would be blamed for the malfunction. As I approached the student to say something, his jumpmaster pulled me aside.

"But," I protested, only to be silenced. "But nothing." said the JM. The student made a judgement call. Yes, he could have kept his canopy and corrected the malfunction, but if you cast doubt on his decision right now, the next time he has a malfunction, he will hesitate. He will be confused. It could cost him his life. He made a choice, and it was a safe decision. Let him have it."

The jumpmaster was right, every bit as much as you were right to reject the takeoff, or ask for an early clearance. Could you avoid wake turbulence? Absolutely. Or not. The controller in all probability isn't a pilot, and has never had to deal first hand with the effects of wake turbulence. You, on the other hand, have intimate knowledge of the effects of wake vortices. You have knowledge, the controller had only published information. Yours wins hands-down, and it's your life. You make the call.

See 91.3

When spraying, we would work often in formation. That put us very close, often near a stall, playing with vortices from the lead airplane; a small single engine ag airplane. More than a few times in that condition I felt the airplane try to roll out from under me at 75' in a steep turn...I can testify that even the wake from another light airplane can be all it takes to alter your entire universe.

You stick to your guns just as you've done. You did nothing wrong, and if the same situation arises, do it again. You are in the right.
OK. How do you all feel about vortices behind a landing a/c? We often get the immediate t/o clearance in our Cessnas behind landing A340, 767, 727, 737, etc. I know what the AIM says, but in real life, I don't think the twr is going to let us taxi 2000 ft down the active for t/o so that we can rotate past their landing point. Should we wait? How long?

I've often been guilty of blindly accepting the clearance and holding it on the ground as long as possible to avoid the vortices. Is it safe and accepted practice to take off with reduced pwr (causing a longer ground roll) until safe? I guess the wait is the best idea because twr is expecting us off in 1000 ft or so for spacing. Curious to hear how everyone else handles it.
Never get bullied by a controller! In SEA the controllers always put you into wake on a clear day. Furthermore, winglets don't mean anything. An A320 (a very clean airfoil) has mini ones up and down and it has rolled me as bad as a DC-10. By the way, it's not just jets that can hurt you. The dash 8 can weigh 36,500 & the dash 8 400 up to 75,000. With their steeper climb graidents than an RJ, the light singles are at an even greater risk.

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