RJ Wake Clearance for Piston Single

[brett]

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?"

"Affirmative."

"Ok, left turn approved."

"Ok, thanks that should keep us clear."

(slight pause)

"I CAN'T CLEAR YOU LEFT, NXXXX TURN OFF THE RUNWAY, TURN OFF THE RUNWAY!"

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.

Opinions?

Thanks,

Brett

 

[AWACoff]

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.
7-3-9
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.

 

[172driver]

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.

 

[generaltso]

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.

 

[bayoubandit]

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!

 

[Ty Webb]

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.

 

[skydiverdriver]

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.

 

[avbug]

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.

 

[172driver]

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.

 

[dashtrash]

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.

 

[TedCFII]

As was mentioned about the Dash 8's..also be aware of the BAe-146/AVRO RJ 85 series as well...Their take-off weights are up in the 30,000s+.... I experience getting *rocked* in the Saab 340 at take off weights of 29,000 lbs on a daily basis departing behind my fellow Airlink brethern... As well as following an A-320....

Just like someone said in a previous post..."If it don't feel right, it ain't right". Wake Turbulence is nothing to take lightly.

 

[AWACoff]

The Bae-146s have takeoff and landing weights much higher than 30,000lbs. Somebody who has flown these could publish accurate weights but 75,000lbs does not seem out of reason...

 

[Mickey]

You did the right thing. Obviously every situation is different and we weren't there with you. Rotation point and winds are a big player in making every situation different. The AIM states that pilots may request additional separation. There is no specified time in the AIM for a small aircraft (you) departing from the same threshold behind a large aircraft (CRJ). In the future you can avoid the dilema by telling the contoller your request for separation before you taxi onto a runway. Seeing the other aircraft on final should have concerned you before you taxied ont the runway. Remember, just because there is a tower doesn't mean that you don't look before you taxi onto a runway. Never be afraid to press the mic button and verbalize a concern.
As far as wake goes, you can get rolled by flying through the wake of another small aircraft.
The BAE 146 takeoff weights start at over 80,000lbs for the small ones (-100) and go to over 90,000lbs (AVRO).
Take care.

 

[brett]

Thanks to all for the advice and opinions!

- Brett

 

[SheGaveMeClap]

A buddy of mine told me the MGTOW on an Avro is in the neighborhood of 94,000 lb.

 

[avbug]

Mickey,

"There is no specified time in the AIM for a small aircraft (you) departing from the same threshold behind a large aircraft (CRJ). "

The AIM is not regulatory, but provides only general guidance. There is a lot of material not covered by the AIM. FAA Order 1770.65M provides, in paragraph 3-9-6 (copied below, for reference) distance separations for aircraft on the same runway.

Advisory Circular AC-90-23E advises that controllers must wait to minutes for separation between a light and heavy aircraft, unless the pilot advises otherwise. "b. For VFR departures behind heavy aircraft, air traffic controllers are required to use at least a 2 minute separation interval unless a pilot has initiated a request to deviate from the 2 minute interval and has indicated acceptance of responsibility for maneuvering his/her aircraft so as to avoid the wake turbulence hazard."

During an intersection takeoff, this time is expanded to three minutes.


3-9-6 Same Runway Separation
Separate a departing aircraft from a preceding departing or arriving aircraft using the same runway by ensuring that it does not begin takeoff roll until:
a. The other aircraft has departed and crossed the runway end or turned to avert any conflict. If you can determine distances by reference to suitable landmarks, the other aircraft need only be airborne if the following minimum distance exists between aircraft:
1. When only Category I aircraft are involved - 3,000 feet.
2. When a Category I aircraft is preceded by a Category II aircraft - 3,000 feet.
3. When either the succeeding or both are Category II aircraft - 4,500 feet.
4. When either is a Category III aircraft - 6,000 feet.
5. When the succeeding aircraft is a helicopter, visual separation may be applied in lieu of using distance minima.

NOTE -
Aircraft same runway separation (SRS) Categories are specified in Appendices A, B, and C and based upon the following definitions:
Category I - small aircraft weighing 12,500 lbs. or less, with a single propeller driven engine, and all helicopters.
Category II - small aircraft weighing 12,500 lbs. or less, with propeller driven twin-engines.
Category III - all other aircraft.
b. A preceding landing aircraft is clear of the runway.

 

[Mickey]

Avbug...
I will restate it this way. The AIM nor the AC90-23E specify any time interval between small aircraft and large aircraft for takeoff separation from the same runway threshold. Why did you bring up AC90-23E. Are you trying to confuse or impress the original poster. AC90-23E reiterates what is already in the AIM(which is a good source of info in one place).
Bringing up FAA order 1770.65M still doesn't answer the poster's question. If you taxi into position and hold after my jet departs and then are cleared to take off, I,m quite sure I'll be off the runway and 6000'ft away from you unless you taxi really fast. You even added info about separation behind heavy aircraft. This is also available in the AIM without having to dig up AC90-23E. The poster didn't ask about heavy aircraft.
Remember KISS. Keep It Simple S.....
I mean no offense but hey. Some people spend way too much time going into details about things that weren't even asked on the original post way too much on this board.

 

[Snakum]

For those relatively new pilots reading this for assistance I'll add my .02 ...

I have been knocked around HEAVILY in a C152 by a departing DC-9 (not the stretch model either) and once thought I was going to die behind a B737 while in a C172 even though I had the required seperation. I don't remember the wind exactly but it must have been such that the vortext was lingering.

Moral ... if you ain't sure ... ask the controller to give you a quick turnout (on TO) or a looooooong landing. In a spam can you CAN GET INTO TROUBLE behind the smaller jets. And if ATC gets testy ... f*ck them.

Minh Thong

 

[avbug]

Mickey,

Why did I bring up other references? Why did you bring up the AIM? That was never a part of the origional poster's comments either.

"The AIM nor the AC90-23E specify any time interval between small aircraft and large aircraft for takeoff separation from the same runway threshold. "

Of course it advises a time interval; that's why I posted it. Didn't you read it? Two minutes, and three minutes if it involves an intersection takeoff.

The suggestion that because something is not in the AIM, it doesn't exist, is misleading. I introduced two other common references to show that it does in fact exist, and that other references are available which may be useful. In point of fact, with direct references to your previous comments, they are useful.

I am trying to impress nobody. The origional poster's questions have been awnsered in full, and the thread has crept somewhat. Simply because every post in a thread is not a direct address to the origional poster, don't get too excited. Life is too short.

"The poster didn't ask about heavy aircraft." The AIM reference you use refers to "larger aircraft", and for certification purposes, any aircraft over 12,500 is a large airplane. Heavy, large, whatever. The poster commented on being asked to depart behind an aircraft that was both considerably larger, and heavier. The point is simple and straight forward. The time intervals specified in the AIM and advisory circular refer to larger aircraft, and do not use "heavy" in the context of the ATC definition of "heavy." Therefore, yes, the origional poster did ask about heavy aircraft, and the question was answered nicely by a variety of different posters.

Note also that "larger" refers to an aircraft which is bigger, with no specific relative difference. Therefore, clearly this refers to the difference between the posters airplane, and the RJ in question.

AC 90-23E is not merely a reprint of what is in the AIM, as it contains more material and is specifically published to address the issue, rather than a small passing reference as found in the AIM.

Take it for whatever it's worth, and I'm certainly sorry it brings you heartache.

Incidentally, AIM 7-3-6(b)(8) advises a two minute interval behind departing or landing larger aircraft...just as it does in AC 90-23E. You'll note that it stipulates "larger" aircraft, rather than simply "heavy."

Finally, the advisory circular does not reiterate what is in the aeronautical information manual. The AIM reiterates what is in other publications; it's nothing more than a general common reference which is compiled from other Orders, Advisory Circulars, Regulations, and Handbooks.

 

[172driver]

I knew avbug would have you for dinner. Wrong guy to argue with!!