Plane Answers: Turbulence causing aircraft to break apart and London holding patterns.

Welcome to Gadling’s feature, Plane Answers, where our resident airline pilot, Kent Wien, answers your questions about everything from takeoff to touchdown and beyond. Have a question of your own? Ask away!

Tai asks:

Hi Kent,

I’m an avid reader of both your blog and Plane Answers and plan to pursue a career in aviation.

I generally keep an eye out in my news feeds for airline/aircraft related stories and came across a CNN article about an Air France A330 which was lost over the Atlantic. Officials are saying that the crash could have occurred as the plane encountered extremely heavy turbulence.

Is it possible for turbulence to be severe enough to actually cause a plane to come down, or would there likely be other factors or problems with the aircraft? Also, if there is turbulence that strong, wouldn’t the captain reroute the flight around it?

I’m often questioned about the dangers posed by turbulence and I’ve explained in the past that modern airliners are engineered to handle the worst case scenarios. But there are absolutely situations, such as extremely large thunderstorms that could cause structural damage to an aircraft.

It’s a big part of why airlines, and pilots specifically, are so concerned about accurate weather reports, good radar technology, flight planning and operating procedures that keep us away from thunderstorms.

Our manual even specifies a 20 nautical mile distance to be flown around thunderstorms. But don’t confuse every cumulous cloud as having the potential of a thunderstorm.

One of the few examples of an airliner being brought down due to turbulence that I’m aware of hits rather close to home for me. In the late 1960s the airline my grandpa had started 40 years earlier purchased a competing airline.

Just weeks after that purchase, one of the recently acquired airplanes, a Fokker F-27s broke up in-flight near Illiamna mountain after an encounter with severe-to-extreme turbulence.

It was the worst accident by far over the 60-year run of the company. So while I’d love to say turbulence could never cause an accident in a modern airliner, I wouldn’t rule it out as a possibility today.

But I’m not so sure that’s what happened to Air France 447. In fact, by definition aircraft accidents are usually the result of something rather unanticipated. So I don’t buy any speculation by the analysts at this point, even with the small clues the ACARS maintenance status messages give us. This is the stage of an investigation where nothing is ruled out.

Jackie asks:

Hi Kent!

What a great service you do here. I have read through numerous posts and it has surely helped calm some of my fears of flying.

A few months ago, I was on a BA flight from PRG to LHR and about 30 minutes outside of London, the captain came on to tell us that due to heavy traffic volume, we were to be placed in a racetrack holding pattern. This holding pattern lasted about half an hour before we began our final descent to LHR. As someone who is a very nervous flyer, anything out of the ordinary makes me very on edge. I’ve flown a great deal, but this was my first experience with a holding pattern. I guess I have been fortunate!

My question is: Just how common are racetrack holding patterns? Are some airports (such as LHR) more notorious for holding planes in that way? Also, I was curious as to whether there is any type of “hierarchy” for exiting the holding pattern? I mean, is it truly first-in, first out? Or since we were in a smaller plane (737 or A320) for the short hop from Prague, would preference be given to the heavies coming from the USA and such?

One final question, when we were in the holding pattern, and in the midst of a turn, the plane quickly jolted/banked to the side in which we were turning and then quickly jolted to the extreme other side as if the pilot quickly corrected this. He then came over the speaker to say that we had hit an air pocket. Does that sound right? Is there any danger in “hitting air pockets” while in a holding pattern turn? I do remember we were pulled out of the pattern to land soon after that experience.

Hi Jackie,

Holding while on the arrival portion of a flight is probably more common in London than any other place I’ve flown. I’d estimate that half the time I have flown into London involved a hold, usually for only one to three turns.

The priority is based on first in, first out. So you may start holding at 16,000 feet and be given lower as the airplanes below you clear out. Finally, at perhaps 11,000 feet, you’d be the next one in line and could then start the rest of the approach.

You almost certainly came across another airplane’s wake. You can think of these currents that are generated by aircraft much in the same way a boat creates a wake as it plows through the water.

In your case, there was probably an airplane holding at the same altitude that had been cleared lower and your flight began holding at that level as well. The wakes usually descend as time goes on, which can be an issue when holding below another aircraft.

Since the holding patterns drawn and flown by the airplane’s computer known as an FMS (flight management system) is so precise when coupled to GPS technology, it’s no surprise that you happened to come along another airplane’s wake.

Generally, they’re startling, but they don’t threaten the safety of airliners.

Coincidently I have a video that shows a flight we did last year as we were about to enter the London holding pattern over “OCK” or the Ockham VOR which is a specific point we navigate to near the town of Guildford. Notice the holding pattern drawn by our computers for our airplane to follow.

In the third to last scene, you can see the airplanes on the screen that we can view in the cockpit. And the final scene shows us selecting a lower altitude before I put the camera away.

Thanks for the great question.

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