Emergency!

It's a beautiful day for flying. The winds are light, the sky is clear, and the temperature is perfect. It's the sort of day where you'd almost feel guilty if you didn't take advantage of the opportunity, since the beginning of fall means days like this are numbered.

It's just a short hop from Wilkes-Barre/Scranton over to Newark. Not even half an hour in the air at 270 knots, and less than an hour from gate to gate. Nonetheless, those few dozen minutes take you through some magnificent scenery, from the Pocono Mountains and the "tricky triangle" of the Pocono Raceway, over the Delaware Water Gap that runs through the Worthington State Forest and marks the border between Pennsylvania and New Jersey, over thick woods dotted with lakes carved out by glaciers 20,000 years ago, to farmland and then cities packed more and more densely before the trip ends just on the other side of the Hudson from the magnificent skyline. What could go wrong?

Well, just like any flight, nothing will probably go wrong, but something always can. And in this case, something did.

We're about 10 miles northwest of the Boonton Reservoir. It's easy to spot from the air, as it has a small island in the middle of it; in fact, it's so easy to spot it's used as a visual checkpoint:

Boonton Reservoir is the lake marked with a flag at the upper left. Newark is the big airport near the bottom right.

How do I know this? Because I'm keeping the general picture in my mind of where we are as the flight progresses. That's nothing unusual; in fact, that's exactly what you're supposed to be doing!

We've already started our descent and begun the pre-landing preparations. Everything is going just as it has on almost all of the hundreds and hundreds of flights I've done before. And then a blinking red light comes...

SMOKE

We have dozens of yellow caution lights for all sorts of minor issues, from the parking brake being set to hydraulic systems to any of the multitude of power sources. These cause a yellow flashing light to come on. We have only a handful of red ones: the ones that are REALLY serious. This was one of the red ones.

This one's job was to tell us that there might be a fire in the cargo compartment. What are we going to do about it?

The same thing you should do every minute of every flight: fly the airplane.

On this particular leg, I was the Pilot Not Flying and the Captain was the Pilot Flying. He did exactly what needed to be done: he flew the airplane while we dealt with the problem. What does "dealing with the problem" mean? The same thing it should mean for you, and the same thing you should have been trained for (and we are trained for every six months):

Don't just do something--sit there!

This is an old aviation adage that has a world of wisdom wrapped up in it. It doesn't mean do nothing, it means do the right thing in the right way at the right time. This is an easy 3-step process:

1. Fly the airplane
2. Keep calm
3. Run your procedures

From the sectional excerpt above, you can see that we were close to both Essex County and Morristown Municipal. Both of them were suitable for landing. We continued past them and on to Newark. Why?

Because we were busy doing those three steps. The Captain was flying the airplane, we were both calm, and I was running the checklist for a smoke warning annunciator. To make a sudden, drastic change in destination would require a whole new plan of action; something probably not best done while in the middle of trying to determine if the back of the aircraft is on fire. One thing at a time: the right thing in the right way at the right time.

While I'm just beginning the checklist, New York Approach spits out in their rapid-fire way a descent, a heading, and a frequency change. Since I was busy managing the checklist, I simply repeated the frequency, ignored the rest, and checked in with the new controller in a calm voice,

"New York, [Flight Number] declaring an emergency. We've had a smoke warning light come on. No further assistance required at this time."

Basically, in a few short sentences, I told ATC--who are a vital part of the team in this--that we have a problem, that it might be a serious one, we're coming to Newark and we need to do it in the most direct way, and we're busy dealing with it so keep the chatter and instructions to a minimum while we handle it.

And that's exactly what they did and we did. They gave us a simple heading that pointed us straight to the airport, gave us an altitude that would set us up on a downwind leg for the runway they would have cleared and waiting for us, and asked very few questions except for the standard souls on board and fuel remaining ones.

In the meantime, I was running through the checklist, informing the flight attendant of the situation and asking her to see whether there actually was smoke coming from the cargo compartment or not, getting the final before landing items done, and so on. After all, this sort of thing has happened to me many times before--except all the other times were in the simulator.

After a couple of minutes, the flight attendant reported that there was no sign of anything unusual. It was likely a false alarm, but we continued to handle the situation exactly the same. Fly the airplane, keep calm, and carry on.

After landing, a half dozen fire trucks were waiting for us on the taxiway we'd be likely to turn off. Notice in my initial call-up above that I never asked for them. I didn't need to: ATC is highly trained too and smart enough to know that where there's smoke, there's fire. All I had to do was tell them our situation and let them do the job of getting the resources supplied.

As we taxied off the runway, I thanked ATC for their help and switched to the frequency the fire trucks use. They made a pass around the plane and saw nothing usual either. They scanned the cargo compartment with their thermal cameras and verified that there was no fire. It was just a bad sensor after all.

Any time a big red flashing light goes off in the cockpit, it's easy to declare an emergency. But what about when things are seemingly more minor? In the next post, I'll get into a bit more about what constitutes an "emergency". See you next Wednesday!


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The author is an airline pilot, flight instructor, and adjunct college professor teaching aviation ground schools. He holds an ATP certificate with a DHC-8 type rating, as well as CFI, CFII, MEI, AGI, and IGI certificates, and is a FAASafety Team representative and Master-level participant in the FAA's WINGS program. He is on Facebook as Larry the Flying Guy, has a Larry the Flying Guy YouTube channel, and is on Twitter as @Lairspeed.

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How to crush something without touching it

What if I told you I can crush a water bottle without touching it? You probably wouldn't believe me, would you? Of course you wouldn't. How can something get crushed without having something doing the crushing?

But I can. I have proof:

Crushed it!

I did not touch this water bottle for at least 30 minutes before I took this picture, and when I put it in that pouch, it was a normal-looking, quite round bottle of water.

So what happened? And how did I crush it without touching it? Well, to be technically correct, I personally didn't crush it; I just set up the conditions for something else to do the actual crushing.)

The thing that did the actual squishing was atmospheric pressure: that invisible ocean of atmosphere that surrounds us. You can't see it, you can't hold it in your hand, and you don't even notice that it is pushing down on you with the weight of an entire bowling ball on every square inch of your body. That thing.

You don't usually notice it at all, since our bodies basically push out against it with the same 14.7 pounds per square inch (psi) of pressure that it pushes in on us with. We're usually in equilibrium with it, so we take no notice of it. Kind of like in-laws who live on the other side of the country: they're there, but we don't notice them.

If the bottle was perfectly fine half an hour ago, why isn't it fine in this picture? Because of something we did in the time in between: we descended from our cruising altitude and landed.

When we were up at 24,000 feet, the pressure inside the cabin was roughly the same as it would be if we were only at 8,000 feet. Think of climbing a few thousand feet up a mountain outside Denver: that's about how thin the air inside the cabin would have been.

By the time we landed, the pressure inside the cabin was a mere 313 feet above sea level, which is the elevation of Washington-Dulles International Airport. So in the meantime, the effective change in air pressure was the same as climbing 7,700 feet down a mountain. There's a lot more air down here. That means a lot more air to push on the bottle.

At 8,000 feet, the atmosphere was pushing on the bottle with a weight of 10.9 pounds per square inch. Because of that, when I drank the last of the water and put the cap back on, the air pressure inside the bottle was 10.9 psi, the bottle was perfectly round, and everyone was happy.

However, by the time we landed, the air pressure was up to 14.6 psi. More air = more pressure on the bottle. However, since I didn't touch the bottle, the air pressure inside it was still only 10.9 psi. Since there was more pressure outside than inside, the bottle collapsed. By opening the cap and letting air in, the bottle would "inflate" back to its round shape, since the pressure inside the bottle and outside would both be 14.6 psi.

If things get crushed as you descend, why wouldn't the bottle start bulging as we're climbing up? After all, the pressure inside the bottle would be 14.7 psi if it were filled at sea level, and back to 10.9 at 8,000 feet. It should do the opposite in the climb as it did in the descent, right?

Right. It does just that, actually. However, the bottle tends to be filled with water and not air on the way up, making less room for the more compressible air. Also, the bottle stretching outward is much less outwardly visible than its collapsing inward. Nonetheless, it is bulging. It's a lot easier to see in the seal on this Pringles can, which was bulging in cruise just before I opened it:

That seal is just bursting with flavor at a cabin altitude of about 6,000 feet.

This expansion and contraction cycle is why your ears pop twice during a flight. On the way up, the air on the inside of your eardrum is trying to push it outward. On the way back down, the air on the outside of it pushes it inward.

Imagine if we could hook up some gears and a meter to the outside of the water bottle. The gears could drive some sort of indicator that shows us how much air pressure is around us based on how much the bottle bulges or gets crushed. That would be a neat way to indirectly measure how high we are.

Don't rush to the patent office just yet, as someone already came up with this idea a long time ago. (Long before airplanes, even. Mark Twain mentions a device using a similar concept in his book A Tramp Abroad, which was written way back in 1880, and the idea wasn't new even then.) There already is something in the airplane that uses this expansion and contraction of trapped air inside a container and puts it to good use. A very vital thing, actually. It's called the altimeter.

Figure 7-2 from the Pilot's Handbook of Aeronautical Knowledge. You can download the entire book for free from the FAA's website. Your tax dollars at work.

That thing labeled "Aneroid wafers" that looks like a stack of discs or an accordion's bellows operates on the same general principle as the water bottle. As the wafers bulge outward, they're connected to some gears that are connected to the dial on the altimeter's face and make the hands indicate the altitude winding upward. As they shrink, the hands start going in the opposite direction. If the aneroid wafers are not bulging or shrinking, you're in level flight.

In the altimeter's case, it's connected to an air pressure source outside the airplane (the static port) so it isn't measuring the air pressure inside the cabin like the water bottle was, but the principle is exactly the same.

When you're learning to fly, everything in aviation seems to run off of two sources of energy: money and magic. While it has always been the case that flying isn't cheap, I think it's an excellent investment because of the magic it brings along with it. Your instruments, however, don't run on magic. They actually run on simple principles of physics that are harnessed in a way that sometimes looks like magic. And it can turn you into a magician who is able to crush things just by looking at them.

See you next Wednesday!

Like Larry the Flying Guy on Facebook:

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The author is an airline pilot, flight instructor, and adjunct college professor teaching aviation ground schools. He holds an ATP certificate with a DHC-8 type rating, as well as CFI, CFII, MEI, AGI, and IGI certificates, and is a FAASafety Team representative and Master-level participant in the FAA's WINGS program. He is on Facebook as Larry the Flying Guy, has a Larry the Flying Guy YouTube channel, and is on Twitter as @Lairspeed.

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What you can't see can hurt you: Avoiding wake turbulence

I recently came across a very nice picture of wingtip vortices. (Unfortunately, it was passed to me without any information on who took it or where. If you know, please let me know so I can give them the credit they deserve.)

With the exception of some NASA tests with equipment designed to help make them visible, these are usually invisible. In the picture below, you get a nice view of what these vortices do to the air, and where wake turbulence comes from. (Throughout this post, for simplicity's sake I'll refer to wingtip vortices and wake turbulence interchangeably.)

Notice the airport in the background.

These are behind every airplane that is creating lift, from a 747 to a 172. In fact, in your training you may have done a nice steep turn, and toward the end of it felt a bump seemingly out of nowhere. That was you doing such a good circle that you hit your own wake turbulence.

If they do this to a thin cloud layer, imagine what they'd do to you if your airplane was in that path. Well, the FAA has made sure you have a scary idea of what they could do, as they point out on pages 13-15 and 16:

"The vortices from larger aircraft pose problems to encountering aircraft. The wake of these aircraft can impose rolling moments exceeding the roll-control authority of the encountering aircraft. Also, the turbulence generated within the vortices can damage aircraft components and equipment if encountered at close range."

This is a very dry, boring way of saying that flying into them can flip your butt over and/or rip your wings off. As exciting as falling head over heels for wingtip vortices might sound, their behavior is fortunately very predictable, which means there's an easy way to avoid them.

Since they're part of the air mass, they move along with it. They also tend to sink. Since we usually try to land into the wind, this means they're coming toward you but sinking at the same time. Solution: just stay above the glidepath of the plane ahead that caused them and you'll avoid them.

I use this quite often when I'm flying the Dash-8. Although at 43,000 pounds it's not a particularly small airplane, it's a wee speck compared to the 767s, 747s, and A340s I've landed behind at Newark. In these cases, I intentionally fly half a dot high on the glideslope.

Notice I said half a dot high. This is on a two-dot glideslope indicator. If you have a five-dot indicator, this is less than two dots. The figure below shows a glideslope indicator that's as high as you need.

Don't use more than this; you don't need to stay extremely high to stay above wake turbulence. It's tempting to do so if you think along the lines of "better safe than sorry", but staying way too high will make the final stage of the approach unnecessarily difficult. If you're flying visually or you don't have a glideslope receiver, use the PAPI lights to help you out. All you need for them is 3 white and 1 red. Again, no more.

At 5 miles out, this is only about 100 feet high. As you get closer to the runway, that gets smaller and smaller. By a mile out (further out than you'd be turning base if you were flying a traffic pattern), this is well under 50 feet. The top part of the following diagram shows you what I mean:

Well, that's great if you're coming in to land, but what if you're taking off behind a monster?

In general, the bigger the wingtip vortices, the bigger the plane. This is actually good news, because the bigger the plane, the more runway it tends to use on takeoff. This means that you can probably lift off well ahead of them. However, that's not the full solution, as the chances are very, very good that they can outclimb you by a lot once their wheels do break the ground.

Now what? Remember that wingtip vortices have predictable behavior, and they move along with the air mass. That means if there's a crosswind, they will slide along the side of the runway. Once you're reached a safe altitude, turn a bit in order to keep them on one side of you. If the crosswind is from the right, the vortices will be moving from right to left over the runway. Just turn a bit to the right to keep them on your left and you'll remain clear. If there's a left crosswind, turn to the left.

Most towered fields where GA planes mix in with the big ones understand what it takes to keep the shiny side up under these circumstances. Not only will they not have a problem with you sidestepping, they will expect you to do it on your own. When they say, "Cessna 1234 cleared for takeoff runway 27, caution wake turbulence departing Boeing 737", they are alerting you of the possibility of encountering wingtip vortices AND giving you implicit permission to maneuver within reason to avoid them.

Although they may make for a pretty picture, wingtip vortices can make for an ugly encounter. By keeping this post's tools in your bag, you can look forward to years of smooth flying!

See you next Wednesday!

Like Larry the Flying Guy on Facebook:

Follow @Lairspeed

The author is an airline pilot, flight instructor, and adjunct college professor teaching aviation ground schools. He holds an ATP certificate with a DHC-8 type rating, as well as CFI, CFII, MEI, AGI, and IGI certificates, and is a FAASafety Team representative and Master-level participant in the FAA's WINGS program. He is on Facebook as Larry the Flying Guy, has a Larry the Flying Guy YouTube channel, and is on Twitter as @Lairspeed.

It takes hours of work to bring each Keyboard & Rudder post to you. If you've found it useful, please consider making an easy one-time or recurring donation via PayPal in any amount you choose.