WARNING: Do not read this lengthy post if you have a COMPLETE understanding of how you will be protected by ATC from a wake vortex encounter.
Everyone knows the precautions to take to prevent a wake turbulence incident on takeoff, right? As pilots, we’re taught from nearly day one of ground school how to stay out of trouble. What if we’re departing from a controlled airport? That means we have extra help in the form of ATC to watch our backsides, right? WRONG.
Let’s use a crash of a number of years ago involving a VLJ as an example of my point.
On June 22, 2006 a single-engine very light jet proof-of-concept, built by Excel-Jet crashed on takeoff at Colorado Springs Airport (KCOS). All involved survived and only a minor head wound was sustained by the pilot.
It didn't take long for lines to be drawn and fingers to be pointed.
On one side was the builder of the aircraft, Bob Bornhofen and his assertion that the aircraft, piloted by Col. James Stewart (USAF, Ret.), encountered a wake vortex from a larger aircraft, which had previously departed from the same runway.
The other side of the line was populated by air traffic control personnel, who insisted they had followed established clearance procedures, holding no culpability in the crash.
As a result of all this, Excel-Jet filed suit against the government, citing negligence on the part of ATC for an improper takeoff clearance, one that only separated the two aircraft by some one-and-a-half minutes. At question was whether the proper type of hold procedure was implemented.
The burden of proof rests with the party doing the suing and as a result, Excel-Jet failed to sway the judge and she subsequently ruled in favor of the government.
Among other things, after spending nearly everyday in the courtroom of this two-week trial, I learned once again that “facts” as presented in courts often bear no resemblance to truth. It’s pure brinkmanship and to the winner go the spoils, and, in this case, junk science risks polluting the ocean of aeronautical knowledge. I’ll not deal with the pollution in this post, but when I do, it will surely stimulate some and bore others.
The following description of some of the facts should cause ALL pilots of light aircraft, or really for any pilot of lighter aircraft taking off behind larger aircraft, to sit up straight in their chair and take notice.
Beware of the Wake
All pilots know that the correct procedure for avoiding wake turbulence from another aircraft when taking off is to wait two to three minutes before rolling or to rotate before the point the preceding aircraft rotated, climbing above the vortex or turning away from it after airborne.
The procedures air traffic controllers follow is governed by a document entitled FAA Order 7110.65. In this document are guidelines prescribing procedures and phraseology for those providing air traffic control services. Specifically, sections 3-9-6 and 3-9-7 deal with departure procedures designed to separate aircraft from the wake vortex generated from the preceding aircraft.
Particularly germane to this case are those guidelines relating to two aircraft departing from the same runway in the same direction, but with one particular distinction: the larger aircraft, a twin turboprop Dassault DH-8-200 (Dash 8) in this case, was cleared from the end of the runway and the Sport-Jet was cleared from an intersection; “an intersection departure.”
This is a vital consideration for pilots to understand. According to the guidelines that ATC personnel follow, if the intersection of the second aircraft is less than 500 feet from the “departure point” of the first aircraft, then no hold is required on the part of ATC.
Did you get that? NO HOLD REQUIRED. Not three minutes, not two minutes, not one second.
The reason for this is simple. The farther down the runway from the threshold you enter, the closer you are to the potential wake turbulence. If you start your roll from the same spot on the pavement as the preceding larger aircraft, presumably you are farther away from danger and you have more options.
What WILL You Do?
This means if you roll up to the hold line at an intersection point on the runway (presumably not at the threshold), you could be given a simple warning of wake turbulence accompanied by a takeoff clearance. What now will you do?
You know from your basic pilot training you are to rotate before the rotation point of the previous aircraft, but what if, for some reason, you don't know where that point is? If you're in danger of an encounter, the controller will issue a three-minute hold, won't they? The answer is “maybe.”
What I learned in this trial is that some controllers follow the letter of the guideline, while others follow the spirit of what’s written. Not always, but often, those who follow the letter are not pilots, whereas those who follow the spirit of the rule typically are. There is a third group: those who make up their own spirit. These are potentially the most dangerous.
This is the exact place where I’ll say what you might expect: the vast majority of people working in the air traffic control system are solidly competent and dedicated people. I trust them with my life.
Without delving into esoterica, and trying not to bore you, there are countless subtleties to all the guidelines ATC personnel follow, and I, quite frankly, never want their job. As a pilot, if you casually read the FAA Order 7110.65 document, you’ll notice that many wake turbulence separation procedures deal with smaller aircraft behind heavies, and since most of us utilize non-commercial GA airports, those heavy instructions can be disregarded.
When you read about smalls behind larges (what most of us encounter) you will come away with a warm fuzzy feeling that all is well in separation land.
With paragraphs like Chapter 3-9-6 “Same Runway Separation,” Section i stating “Separate a small aircraft behind a large aircraft taking off … by 3 minutes unless a pilot has initiated a request to deviate from the 3−minute interval. In the latter case, issue a wake turbulence advisory before clearing the aircraft for takeoff.”
Chapter 3-9-7 “Wake Turbulence Separation For Intersection Departures,” Section a stating: “1. Separate a small aircraft taking off from an intersection on the same runway (same or opposite direction takeoff) behind a preceding departing large aircraft by ensuring that the small aircraft does not start takeoff roll until at least 3 minutes after the large aircraft has taken off… 3. Separate a small aircraft weighing 12,500 lbs. or less taking off from an intersection on the same runway (same or opposite direction takeoff) behind a preceding small aircraft weighing more than 12,500lbs. by ensuring the following small aircraft does not start takeoff roll until at least 3 minutes after the preceding aircraft has taken off.”
But then there’s this seemingly innocuous paragraph: 3-9-7, b. The 3−minute interval is not required when: 2. “The intersection is 500 feet or less from the departure point of the preceding aircraft and both aircraft are taking off in the same direction.”
This is critical, but I’m not going to go into detail here. Why? Because you only have to know one thing: Different controllers use different methods and interpretations of “Departure Point,” and at best that’s bad, but I believe the largest flaw is not in how controllers interpret, but in the guideline itself.
The logic behind this is that since the distance is less than 500 feet, it’s practically the same as a non-intersection departure. So, at that point (and in this specific case), 3-9-7, b. 2. should refer back to 3-9-6, i, which requires a 3-minute hold.
I'm Not My Brother's Keeper
Now, to what really boiled my blood at the trial. When the controller-in-question was interviewed on the stand, some of her answers concerned me deeply.
What follows is my impression and not necessarily a statement of fact of the personality of the “offending” controller. Most people who can read other people well would size up this person fairly quickly. This controller is an intelligent and “precise” sort of person, who might find it difficult agreeing that they were wrong about something – after all, before utilizing a procedure, this person seeks to understand all the necessary details so they might be fully equipped to offer sound and discerning judgment when needed.
On a personal level, I can live with a controller interpreting in ambiguity, but one thing that rings from my early training are the words of my instructor, “An attitude precedes an accident.” And that’s what I believe is one of the contributing factors here.
When asked about the reasoning behind the guideline, to separate vulnerable aircraft from wake vortices, and why she hadn’t given a three-minute hold and why she hadn’t observed where the preceding aircraft had rotated and whether she realized she was sending this small aircraft into harm’s way, her reply was that it wasn’t her concern. She followed the guidelines and gave a proper clearance, end of story, wipe my hands.
As stated earlier, I believe this attitude is the rare exception and not the rule, however, if the ambiguity in the guideline is not clarified, then it won’t matter how well meaning a controller might be – someday, somebody will die.
One thing I haven’t talked about is the pilot’s responsibility. It’s true, the ball of responsibility rests in the lap of the PIC. Don’t let the all to common “Caution Wake Turbulence” warning become a din in the background. If your ears hear “wake turbulence” at any time, snap out of it and think carefully. YOU request the 3-minute hold – it’s your option. YOU request the go-around. YOU don’t assume ANYONE’s got your back. Stay safe and stay alive.
Thoughtfully Submitted by Jeff Mattoon
