Silver Wings Then other Things: Part 4.


This is the final installment of a 4 part series putting you in the captain’s seat of an airliner.

Want to start at the beginning? Click here.

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It’s the top of descent. You just kind of get the feel, just know we’re getting to that point, if you’ve been engaged in the flight, where the natural rhythm of things is to start descent.

Used to have different cues that signaled the top of descent point before we had the precision of dual Inertial and multiple GPS systems tied to multiple flight guidance computers figuring descent rates and distances down to a gnat’s ass. One that was nearly infallible:

No, they didn’t call up front and suggest descent. They went into the First Class lav near the cockpit and unleashed a cloud of hairspray and fu-fu to get ready to look great in the terminal between flights. They always somehow just knew it was about time to touch up the war paint and big hair–which was our clue up front that “hey, must be time to start down.”

 

"Uh, Center, we're ready for descent."

The descent is fairly standard, an exercise in Euclidian geometry (want more details? click here) that takes into account altitude, distance, speed and fuel flow. But the approach and landing planning started before take-off.

Driving in to the airport, I have in mind the basics of the destination airport (or airports, on most days). At this point in my flying career, there are few airports in our domestic route system that I haven’t already landed a jet on, so I go back over what I know: airport altitude, terrain, runway length, runway surface approach types, traffic conflicts and a few other details.

I like to use Mexico City as an extreme example, because it shows that there’s really no “one size fits all” with those factors above: MEX has a 12,000 runway, but the airport elevation is 7,300 feet. So despite the long runway length,  aircraft performance and maneuverability are reduced by the high pressure altitude–not a good thing when flying slow and dirty as you must to land–the higher true airspeeds at altitude have you touching down with a hell of a ground speed, making this long runway a challenge for stopping nonetheless.

And that’s on a runway that is neither crowned nor grooved, which means any rain will likely pool and stand, screwing your brake effectiveness, and the mix of moisture and reverted rubber, which you know from experience seldom gets cleaned off south of the border, will make stopping a real challenge.

Meanwhile, Santa Ana “Orange County” Airport is at sea level, with a crowned and grooved runway–but it’s only 5,700 feet long. As a comparison, the take-off runway at DFW is 13,000 feet long. Stopping the jet at Orange County is as dicey as it is at Mexico City.

Most airports fall somewhere in between, but runway length and airport pressure altitude aren’t the only factors to consider. The wild cards are always the weather and the runway surface condition: all 13,000 feet at DFW are about as useful as the 5,700 at SNA if the runway is slick from rain, sleet, snow, or ice. There’s no free ride on landing.

Plus, add this, would-be Captain: you don’t know what you don’t know.

There are those who think because a runway is long, clean and dry that stopping can or should be a leisurely affair: some copilots have actually pre-briefed “I’m going to use minimum braking or reverse and let it roll.”

The hell you say.

No matter what runway you land on, there is a certain landing distance required due to the kinetic energy the brakes must absorb to stop the tons of metal, fuel, bones and blood still thundering forward at flying speed. Whether that distance is 3,000 feet or 8,000 feet, it makes the most sense to take care of the kinetic energy right away.  Once it’s absorbed and the jet decelerated, you can do whatever you want with the runway remaining.

Remember the basic lesson of flight, and the number one item listed as useless to a pilot:

“Runway behind you!” It’s useless, wasted, history, toast. If you’re still rolling without braking properly, you’re toast if anything goes wrong after touchdown.

And there ain’t no ‘splaining it to the FAA after you don’t stop on the runway.

Same goes for the knuckleheads who float a thousand feet or so down the runway fishing for a smooth landing: heretics!

Here is what God has told us about landings:

No floating, easing it down. On speed–neither too fast (more kinetic energy) nor too slow (high nose angle, possible tail strike) and within the zone Moses above is stressing–even though aircraft were for him still a couple thousand years down the road.

Look, can we speak frankly as pilots here? Who the heck cares what the passengers say as they deplane? They have no idea what a good landing is and even if they did, from where they’re sitting, they really have no way to tell if you’re on speed and at the right point. I’ve seen them get off saying, “Good landing” when I know the actual landing was too far down the runway and not on speed.

Forget about them and their ignorance–you have a job to do: on speed, at the correct touchdown point and sometimes, firmly: if the runway is wet, we don’t flirt with hydroplaning. I don’t give a damn if to the passengers it feels like everyone in China just jumped off a chair–we plant it, stop it and taxi to the gate.

Okay, time out: are you easily bored? If so, skip down to below the math (I really hate math too). If not, read on.

Engineering data shows that hydroplaning is most likely at the speed that is 9 times the square root of the tire pressure. Our main tires are at around 205 PSI. So, 9 x 14.32 = 128.88 knots as the primary hydroplane zone.

So the smart money gets the plane slowed below that speed as soon as practicable, because whatever runway there is behind you is no help to you, and whatever runway there is ahead may have an added hydroplaning factor you could have avoided: a puddle, a slick of reverted rubber; whatever: stop now, play smooth pilot later.

That formula works for your car, too: 9 x 6 = 54 mph as your primary liability to hydroplaning–and like in a jet, don’t give up: once you get through that speed zone via smooth deceleration, you will get control back. Too many people on the highway and on the runway think that once hydroplaning starts–that’s it. Stay with it, you will slow and regain control. And that is today’s

Okay, we’re back. So God gave Moses this to help him:

Autobrakes: the greatest advancement in commercial aircraft since flight attendants gave up on big hair (breathe easy on top-of-descent). The “RTO” setting is for “Rejected Take Off,” or abort. We’ve talked about that recently. You don’t subscribe? That’s a shame.

Then the 1,2 and 3 settings provide graduated brake application depending on stopping distance. Then there’s “MAX,” which is an acronym for “Holy Shit.” I use “Holy Shit” on the ultra short runway, or the ultra-long like Toronto in a blizzard when the  tower says, “Cleared to land, you’re the first, it’s mostly plowed, let us know how the braking is.” Remember, there’s no “one size fits all.”

At any point, you can take over braking manually simply by pressing on the rudder pedals. But especially if you’re using differential rudder, it’s best to leave them on as they’re not prone to apply asymmetric braking as would be likely if you were pushing one rudder pedal more than the other for crosswind crab control. I usually override the autobrakes slowing through 100 knots as we near runway high-speed turn-off speed (80 knots). And if you use  the “Holy Shit” setting, you’ll need to add power to taxi off the runway. That’s a good thing.

Now, you’re fifteen miles out, maybe 5,000 feet high (okay, more math: a three degree glide slope allows a civilized descent rate of 700 to 1,000 feet per minute depending on the ground speed, so three times the altitude is a good distance to begin descent). Slow to below 200 so you can “throw all the shit out,” as one of my SWA pilot buddies says, referring to the gear and flaps. The flaps have a bunch of limiting speeds, and 190 is below most of ’em. Makes it simple.

If you’re the lucky guy in the left seat of a 737-800, you don’t even need to look inside from this point on, except to verify gear and flap positions before landing.

Now it’s a matter of guiding the jet down the glide path, touching down in the correct touchdown zone, then braking smartly and efficiently. Got it?

Enough blabber–want to watch it all come together?

This video was passed to me by a friend of mine a few years ago. He was killed last Spring in an ATV accident, but his memory lives on with those who knew him in the Air Force and afterward. The video was not shot from the aircraft type that I fly, but it’s an airport I’m very familiar with, and it has many of the complications we just talked about. A tip on the video: if an ad pops up, just click on the “x” in the right corner to get rid of it. And if you click on the triangle above and just right of the “360p,” you can choose a higher video quality.

Now, take all of the factors we’ve just gone over into consideration, then turn the approach and landing into a symphony. Please remain seated till the aircraft comes to a complete stop, and thanks for flying with us today.

Coming Soon:

What do the sixth graders of Miss Giulia’s class in Ottawa want to know about flying?

Cool stuff! Stay tuned . . .

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5 Responses to “Silver Wings Then other Things: Part 4.”

  1. Dr. Asoka Dissanayake Says:

    Thank you.

  2. Hello

    I really enjoyed this series. You are a great writer and even with all the tech speak, I understood everything you wrote about. I love reading from a new perspective. You did a great job telling the story. Well done.

    I sat here the other night and ran through hours of You Tube video of the A-380 and other aircraft takeoffs and landings. It’s all very magnificent.

    Jeremy

  3. Another great post, Chris. It certainly covered most of my questions abouot braking. I can appreciate why the RTO setting is clicks away from those used for landing. My quess is that RTO braking is going to flatten your eyeballs on the windshield. I guess the anti-skid feature is different from AutoBrake and is a much closer relative of the automobile’s ABS (Pulse pulse pulse to avoid a full lock-up). So, does your AutoBrake disarm at about 80 Kts, or do you have to tap t he pedal? Otherwise, you’d have a full stop on the runway. Perhaps good in some situations, but not greate for routine traffic flow. Am I close? I’ve also learned that REVERSE is not part of your landing (stopping) distance calculation, but a bonus. (I’m not that sharp, but I’ve had some other assistance.) I appreciate that this last question is not fair nor realistic. I’ll provide the variables. When properly applied, roughly what percent of braking function does REVERSE provide? Your current aircraft, Max landing weight, Sea Level, correct approach speed, still air, temp is 45F, touch-down just before 1500′ and unlimited clean, dry runway, AND you still want to stop ASAP, using Auto3. A rough guestimate will answer the question. Thanks again. An interesting reading experience.
    -Craig

  4. Like this series of posts! I’m in ATC. Thanks for sharing from a pilot’s perspective of the whole process from preparation to touchdown. Keep blogging. 🙂

  5. Thanks, Chris, for a great ending to your 4 part series. I enjoyed it.

    And…it’s nice that you honour the memory of your friend by sharing his videos…we enjoy them immensely. Thank you. 🙂

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