Wake Turbulence: Small behind a Large

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DCR

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Hello,

Just reading AIM section 7-4-9 and noticed there is no guidance for a small taking off behind a large, if both are making a normal departure from the threshold.

This is a common situation I encounter at my home base, and usually I just hit the gas when ATC releases me. However, it is a Delta so separation is completely on me (pretty sure about this - correct me if wrong).

When driving your trusty ol' C172, what do you think is a safe time to wait if departing behind an A320/321, B737, Gulfstream V, Bombardier (CL60), etc.?? Would / do you ask for a delay from ATC?

PS: There is guidance for opposite direction or intersection takeoffs, but I have never seen that.

PPS: Those are all "Large" aircraft per FAA's definition which I see at my base.
 
Wake vortices sink and drift downwind. I recall being taught that, under most loading conditions, our aircraft types will lift off sooner and climb at a steeper gradient (ft/NM, not ft/min) than almost anything that could make a wake strong enough to concern us. As a matter of extra caution, you could turn 10 degrees upwind until you're far enough away to no longer be concerned.
 
Nah, unless you’re behind a 757, separation is basically on you from a threshold take off. ATC is using 6,000 ft SRS sep for you (cat I) behind the large (cat III) but that’s about it.

Threshold and opposite direction can be 2-3 minutes depending on type of large but some of that’s waiverable.

If you want more time, just say you’d like 2 minutes for wake turb. Unless the airport is super busy, they shouldn’t fuss.
 
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Good points.

Do you make any special adjustments if following a large on approach to land? The recommended separation there is 4 nm, but I don't even use an EFB (yet - working on it) so I'm just eyeballing everything.
 
DJTorrente said:
Wake vortices sink and drift downwind. I recall being taught that, under most loading conditions, our aircraft types will lift off sooner and climb at a steeper gradient (ft/NM, not ft/min) than almost anything that could make a wake strong enough to concern us. As a matter of extra caution, you could turn 10 degrees upwind until you're far enough away to no longer be concerned.
Click to expand...
Hence, takeoff or approach, stay above a big, heavy's flight path.
 
DCR said:
Good points.

Do you make any special adjustments if following a large on approach to land? The recommended separation there is 4 nm, but I don't even use an EFB (yet - working on it) so I'm just eyeballing everything.
Click to expand...
I stay above their glide path and touch down after their touch down point.
 
DCR said:
Hello,

Just reading AIM section 7-4-9 and noticed there is no guidance for a small taking off behind a large, if both are making a normal departure from the threshold.

This is a common situation I encounter at my home base, and usually I just hit the gas when ATC releases me. However, it is a Delta so separation is completely on me (pretty sure about this - correct me if wrong).

When driving your trusty ol' C172, what do you think is a safe time to wait if departing behind an A320/321, B737, Gulfstream V, Bombardier (CL60), etc.?? Would / do you ask for a delay from ATC?

PS: There is guidance for opposite direction or intersection takeoffs, but I have never seen that.

PPS: Those are all "Large" aircraft per FAA's definition which I see at my base.
Click to expand...
AC 90-23G
 
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Get off the ground before the big one left the ground. Offset slightly up wind.

If any doubt, ask for a delay in takeoff. Nothing wrong with that. WT can destroy your airplane and kill you and your passengers. Make decisions that keep you safe, and free from a lifetime of guilt.

At a local airport I have had the controller hold me for a few minutes after a heavy took off.
 
I always ask for a delay if taking off or landing behind a big, heavy airplane. I once had a controller being an a** about it but other than that one time, they’ve always been super nice and accommodating to my request.
 
I don't trust the accountability of any others besides myself. I was taught wake vortices sink at 500 ft/min and dissipate in about 2 minutes. I'll ask for a delay or immediate turn if I'm right behind something big - since I probably can't out climb its departure. I had to reject take off clearance once because tower couldn't give me an immediate turn behind a Global 7500 and wanted me to go while it was still over the departure end of the runway.
 
I've hit wake turbulence at altitude. Small 737 making approach to KPAE (Paine Field, WA) six or seven miles from the runway. I flew under its flight path at right angles about 60 seconds later heading west to Whidbey Island. It was a sudden roll excursion, compensated for. It was dangerous only in that it was surprising.

It could easily have been much more serious if I had crossed the 737's flightpath sooner or had been close to the ground.
Wake turbulence from even a small heavy can toss one of our little spamcans around violently. I'd rather **** off ATC than take the risk.
 
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