November 26, 2008 by Bruce Landsberg

Wake turbulence is one of those ever present threats that we’re all aware of but much too savvy to get caught up in. The most recent incident involved a Lear 45 on approach to Mexico City that crashed several weeks ago when it go too close to the Boeing 767 it was following. The last radar hit showed just over four miles separation when five miles is considered the minimum. The cockpit voice recorder transcript dramatically showed how quickly things can go from boringly normal to completely out of control in literally seconds. There were nine fatalities on the jet and five on the ground.

I’m personally not convinced that one mile further back would make that much difference – the main thing is not to be below the lead aircraft. Back in the late 60’s and early 70’s FAA did a lot of testing on the phenomenon. The test pilot comments should be sufficient motivation to absolutely avoid the big rollers.

Danger exists not only on arrival but departure as well. I once refused takeoff clearance at Atlanta’s Hartsfield airport when ATC wanted me to follow an MD80 on climb out. The Super 80 may be a pig, according to some who fly them, but a Bonanza will not come even close to out climbing one. I had asked for an immediate turn out which ATC refused, so I refused. Since I was in holding position on 9L and royally gumming up the works, the controller suddenly became reasonable and saw things my way. No penalty, no foul, just a need to understand the physics involved.

If you fly where the big guys roil the skies remember that distance, altitude (above) and alternate flight paths are your friends.

For a quick review, take the ASF quiz on wake avoidance.

Special thanks to pilot/photographer Steve Morris for the great wake picture.

Epilogue to last week’s blog on prop safety: A student pilot was was killed last week when he hastily departed a Cessna 150 flown by another student, upon fear of being discovered of flying illegally together. Note to self: Don’t fly illegally and certainly don’t attempt exit through a spinning prop.

Bruce Landsberg
Senior Safety Advisor, Air Safety Institute

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  • instrctrpilot

    Remember to look for heavies en route as well.

    Many years ago, while working as an investigator for a law firm, I was flying the boss with his toy puddle on his lap. We were in his turbo V35, VFR, though on an IFR flight plan, over LAX at 10,000 ft en route to San Diego for a trial. Flying in smooth air we hit what I initially thought was clear air turbulence that dumped us 500 ft almost instantly. The puddle got to practice weightlessness while the boss and I tried to recover our whits and figure what happen. I finally saw a 747 climbing in the distance, about 10 miles out. We must have crossed its climb at a 90-degree angle and hitting wake turbulence. No heads up from ATC; who knew. Good thing we hit straight on. I don’t know if one wing could have withstood asymmetric loading at cruise speed if we crossed at a shallower angle.

  • Jon Hooper

    Bruce – If you had climbed out at Vx your speed would have been at least half of the MD80’s. I don’t believe there is any way you could have intersected his flight path. Consider also that the MD80 uses about a mile more runway to get off the ground.

  • Airline Pilot

    Bruce- It seems that you are one of those guys that think they can get it done at any cost? I have flown the MD80, B757, and B767. If it doesn’t feel or look good then it’s better to wait! What IF his engine lost power, or gear would not retract, or ? One thing will not get you killed, but two or more things happening at the same time? Sometimes you just need to say “NO”. Use good judgment and you will have a long and safe flying career, and even then you will have the stories that others talk about.

  • Art Brothers

    Long before this came to our attention I was heading south on the east side of the San Francisco Bay in a Cessna 190. Observed a (747?) passing above and to my left descending to pass way ahead of me as he turned right on final to SFO.
    The heavy was close to or already down when I got hammered with a violent near upset. impact. Back to smooth – and thought it was what we later came to call CAT. That lesson has been shared with many – and my opinion is to give the big boys air behind them lots of time for the wake to dissipate.

  • Airline Pilot

    Sorry Bruce- The comment was directed at Mr. Hooper

  • Fred Ashman

    I concur with staying above, or laterally away from a big jet’s flight path on arrival and departure. My encounter occurred on a clear, totally calm VFR morning into PHX, following an L1011. We were in a Cherokee Six. Having flown frequently into LAX I was familiar with avoiding vortices. I requested and was given extra separation (we were 9 mi in trail) and flew the approach above glideslope for avoidance. At about 1200 AGL the airplane violently rolled left to near inverted. The control yoke was pinned for about 4 seconds. The impact was so violent it felt like we had been in a midair. I recovered and rolled level at about 600 AGL. The tower saw what happened and cleared me to land on any runway. After an uneventful landing I immediatly called and requested an investigation. We found out the L1011 had “platformed” high and hot, with flaps and nose up to bleed excess air speed. With no winds to dissipate the vortex, the spinning air desceneds at about 500fpm. Just in time to catch and toss us around like a toy. Conclusion, always ask for extra spacing AND verify preceeding big jets were on glidslope or not. If not, exit the pattern and get resequenced.

  • Fred Ashman

    correction re L1011 configuration: …with flaps DOWN and nose up,,,

  • Larry Burson

    Landing a B-727 at PHX in the 1970s, was the worst experience I had with wake turbulence. It’s a helpless feeling. Wind was calm, heavy traffic ahead was already well clear of the runway, and we were about 500 ft AGL. Plenty of legal separation, but the lesson has stayed. In clear, calm air wake turbulence lasts a looooooong time.

  • Bill Culwell

    Flying a 182, west bound for PHX and north of El Paso in extreme vfr and level at 10,500, center advises us of a flight of two B-52’s at our 3 o’clock , southbound, and desending out of 12,000. No joy and then there they were….. oh my, they are big and beautiful…… they pass directly overhead……. then it hits me……. WAKE…… what to do…… so i turn the auto pilot off…. reduce power…. and wait for what i’m sure won’t be fun…. nothing. no buffet. ‘no nothing’ …… i think it was our lucky day….. i’m still not sure of what the correct action should have been. Any advice is appreciated….

  • Bob Downs

    Sometime in 1954, I took off in a C-54 (DC-4) close behind a C-47 (DC-3) from Eglin AFB, FL. We were close to our 72,000 lb. gross weight so I had a long roll in the hot, humid air. Shortly after lift-off, I got thrown into a nearly vertical bank by something in the air. We didn’t know anything about wake turbulence, but I don’t know what else it could have been even though the C-47 checked in at about 28,000 lbs, hardly a heavy by any definition. But I’ve since assumed that any airplane of whatever size can create a serious problem. 40 people came close to dying that day. bobd

  • Pilithigh

    If they are directly above there is no issue. If they had been 1000 feet above and you had crossed their path two minutes later you you would have been in for a ride of your life, however. If you think that you may be in the wake turbulence region, Va (maneuvering speed) for your airplane would be the best speed.

  • Pilithigh

    Several years ago I was flying a L-1011 on final 3 miles behind a B727. At about 1000AGL we were rapidly rolled to 30 degrees of bank from the vortices of the 727. You don’t have to be smaller than the preceding airplane to be affected. A 727 has very strong vortices.

  • Marty

    Bruce, Can you share a web link to the voice recording, or a transcript of what was said in the Lear? Many thanks, Marty

  • Nicolas

    I’m convinced that wake turbulence is one of the biggest threat we are exposed to. The time they can last in some atmosphere conditions (still and stable air) is such that even augmented seperation will not keep you safely clear of them.
    I have in mind four examples, at low and high levels that make me very cautious about it.
    I don’t know were the limit is, as one of these encounters occured over the south Atlantic in a B747 after one hour in the cruise.
    We obviously flew about 90 degres through the wake as there was two consecutive up and downdrafts. The vertical acceleration was such that several passengers and flight attendants were injured, some severely and the flight had to be diverted for medical assistance. No damage was found on the aircraft.
    Same kind of situation was encountered during a night patrol at high level in a Mirage3 fighter aircraft.

    Use your jugment and don’t hesitate to ask for, or take the necessary delays and spacing necessary to keep you clear of wakes.

    High pressure days with light winds, especially around 5 Knots cross-wind and any tail wind during final approach should raise high concerns. Try to integrate the wind pattern and the runway configuration with what you know about the typical path of wake turbulences, and manage your flight path accordingly.

    If you’re unsure don’t take a chance… stay away from this invisible killer.

  • Paul S.

    Five or so years ago, while on the Expressway Visual to 31L at JFK, I was in a King Air several miles bedind a Boeing of some description. I was instructed to cross a fix at a certain altitude, the same instruction given to the Boing in front of me. As I descended, I was thinking that maybe it would be good idea to stay a tad higher. Unfortunately I did not stay higher, and descended to the altitude just before the fix. When I got there I felt the hardest single thump I have ever felt in an airplane. It really shook up the passsengers. From then on If I have an idea that ATC instruction may not be in my best interest, I begin to negotiate an alternative immedately and DO NOT blindly accept the clearance.

  • Greg McIntyre

    I fly a Cessna 310R. It seems we are always vectored in behind the heavys with keep max speed and caution wake turbulence cleared to land etc. As soon as you accept the clearence, contollers are no longer responsible for any consequences.

    I have had several minor encounters with wake turbulance over the years and it is very unnerving.

    You have to ask, why do the controllers place us in this situation?

    I know airports are busy and everyone wants to be on time but is it worth the lives of crew and pax?

    Would better understanding and more education be warranted?

  • Francisco


    I am not a Lear Jet rated pilot, but I have talked to some Lear 45 rated pilots and all of them think that was not the cause. What do you think?
    Was the lear 45 flying lower than the Boeing 767? It seems that if the Lear was 4 miles apart in bound for landing, then it was higher than the boeing 767.

  • Bill Seymour

    Bruce, on a typical arrival into Charlotte (CLT) the airliners are kept at 11,000 and turboprops at 10,000. I often watch as a big Boeing or Airbus flies directly overhead of my Pilatus PC-12 by a 1,000 feet and perhaps 40 knots faster. This eventually places the airliner out in front and above me. This would seemingly place my aircraft in position to experience wake turbulence, though I have been fortunate not to encounter same in the arrival environment. Charlotte controllers are alert to warn of wake turbulence but might this procedure be a dangerous one. Your thoughts please.

  • Eric Davis

    As a low-time VFR private pilot flying near the Hartsfield class B (PDK is my home airport), I have developed an appreciation for separation and avoidance.

    Sadly, I log way more time annually in a commercial cabin. As a passenger, with knowledge of the dangers of wake turbulence, I am concerned by what I perceive to be a lack of spacing on departure at ATL.

    Many times I’ve been in the cabin of a CRJ following a much heavier aircraft in just the time it takes for the pilot of the CRJ to roll across the holding line, line-up on center, and accelerate. I realize that the CRJ is going to take to the air much sooner than the heavier aircraft before it, but to Airline Pilot’s point about multiple problems on take-off, it seems that this practice leaves little margin for error.

    I understand the business reasons for such tight spacing. However, I would feel better knowing what contingencies exist, or practices are in use, to prevent encounters with wake turbulence in this environment.

  • http://none kerry caramanis

    Very interesting comments, resurrected memories of an encounter I had at 1000 feet in Southern Cal in the early 80’s. A pilot friend and I where over the Catalina channel in a rented C172 a few miles west of the coastline looking forward to our anticipated $100. buffalo burger at Catalina Island.

    It was a beautiful CAVU day and we were enjoying the beautiful SoCal coastline views with Catalania Island about 20 miles ahead at our 12 o’clock, when the aircraft made a violent roll to the right, about 20 degrees then whipped to the left almost vertically. The turbulence lasted less than five seconds. I regained control and my thoughts immediately went to CAT as the cause, when we suddenly spotted a heavy at 10 o’clock high estimated to be at about 10,000 and climbing. We had no further doubts as to the cause of our unintended acrobatic maneuver.

    That was an e-ride I hope not to repeat and have since paid close attention to avoid close encounters of that kind.

  • Fernando Russek
  • Albert

    For those of you who wish to see what went on. Go to youtube and type XC-VMC that is the tail # and you will see the acual radar video and hear the CVR as it happened.

    God bless their souls.

  • MAG

    Bruce, I think you made a very good desicion!.
    And for Mr.Hooper,not a very wise comment.

  • stinky

    Wake, shmake. I was four minutes away from where the plane dropped. Before the Mexican government censored everything the next day, the news media reported the truth. The Mexican Secretary of the Interior was on that plane and was MURDERED. Probably shot down or bombed. There is a drug war (in reality a civil war) in Mexico, and it’s taking a huge toll. Dozens upon dozens of witnesses said the plane was on fire before it fell. Perhaps the reason why there is a voice recorder “transcript” but no recording shown to the public. I’m not going to get into speculations, but there is A LOT more than meets the eye to this story, including a drug laundering investigation in Spain. One thing it WASN’T: WAKE, for damned sure.

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