Wednesday, November 30, 2005

Instruments of Torture


There is school of thought that finds the perfect expression of a pilot's art in the kind of bush flying that keeps the Alaskan economy running. This is a seat-of-the-pants kind of flying where the pilot is at one with the machine, an intimate and highly skilled type of flying that has airplanes doing the work that can't be done otherwise, and pilots doing a job that most people cannot do. Many bush pilots learn to fly at a young age, and many fly an airplane with virtually no flight instruments. It's a pretty dangerous, intuitive thing, but it embodies a lot of what most pilots think of as their core skill.

But bush flying is a very different job than what almost any commercial pilot does down here in the Lower 48, however much we try to think those pilots are somehow like us. A crop-dusting pilot may understand the bush pilot's job, but the flying realities for an airline pilot--the regulatory environment, and the jobs to be done--just hardly cross paths with the world of bush flying. The airline world is as safe as it is because what seems (to a geek like me) magical and impossible is in fact highly regulated and codified, and there is little room for improvisation. The safety demanded of an airline pilot would make a bush pilot's job simply undoable. I have no bush flying experience, though as a pilot I understand how it differs from what I know. But the airline pilot's job I know.

An airline pilot's world centers less around reading the weather (if it isn't a thunderstorm, we're gonna fly in it regardless) and flying on the ragged edge, and more on Air Traffic Control (ATC) and instrument flying procedures. And it's this instrument flying business that I want to talk about. (Aside: I thought about this the other day after a comment on Lizzie's blog. Is this a sensitive subject? Am I giving away State / Trade Secrets? But no. Any fool can go to an airport or a Barnes & Noble and buy a book on instrument flying, or attend a groundschool. I ain't sayin' nothin' new.)

It is impossible to fly an airplane without reference to the horizon. I think almost everybody polled at an airport would not understand this. But it's the god's honest truth. At the very best, a person can keep upright in the clouds without help for a minute or two. And any attempt to hold a precise altitude or heading without visual reference is simply, unequivocally impossible (I've done my own experiments as a flight instructor to verify this). Even the simple task of keeping wings-level and shiny side up in the clouds is plainly beyond our capabilities without some kind of cockpit instrumentation. Our senses are evolved for orienting ourselves relative to terra firma and gravity's arrow; we simply don't have the senses needed to fly without help. A bush pilot just stays out of the clouds, period. But we airline dogs don't have that luxury.

To counter this problem, we have a pretty standardized set of flight instruments in any airplane, large or small; and the design of this suite of instruments is a fabulous and beautiful thing of economy and overlap. This particular suite of flight instruments was perfected and standardized sometime before and during the Second World War (I have a book at home which talks about this stuff, but the book is in Wisconsin and I'm in Houston; so we'll have to just bullshit our way thru. All dates are approximate!), and has remained largely unchanged until quite recently. (It's an interesting and recurring fact of history that most problems will be solved when military money is put to them; almost all aviation advances have come to the civilian world by way of military contracts, and this is no exception.) This instrument set sits directly in front of the pilot in plain view, and we spend much more time looking at this instrument panel than we do looking outside or anywhere else inside.

This suite of six instruments is arrayed in a "six pack" configuration, three on top and three below, and consists, without too much variation, of the following: a gyroscopically-stabilized artificial horizon (AI, for Attitude Indicator), top center; a barometric altimeter, top right; an airspeed indicator (ASI), top left; a gyro compass (DG, for Directional Gyro), bottom center, below the AI; and on either side of the DG, a vertical speed indicator (VSI), and a gyroscopic rate-of-turn indicator with a ball-in-glass inclinometer, this latter often called a slip / skid indicator. I won't discuss the instruments in individual detail except to say this: every kind of information needed by a pilot--pitch, roll, yaw, airspeed, heading, attitude--is available in this suite of six instruments, either directly or by inference, from at least two sources; so one can lose one or two instruments and still remain safe and in control. The choice and design of the specific instruments ensures this with a beautifully-evolved economy (and, true to form, pilots spend most of their time in training dealing with stuff that's broken or malfunctioning, even though flight instruments in actuality are almost foolproof).


(This is a panel of a Cessna 172, a typical basic instrument trainer. The gauges to the right of the six pack are navigation instruments.)

To these "basic six" are added a wet compass, navigation instruments, Traffic Collision Avoidance (TCAS) systems, communication radios, and of course whatever other aircraft system gauges and controls are deemed necessary by the aircraft designer.

The Instrument Rating, which is the training needed to understand, and to control the airplane by way of these instruments, is far and away the hardest rating for a pilot to acquire. Something like 70% of pilots seeking an Instrument Rating do not succeed. It is an intensive and time-consuming process, and one which requires constant practice to keep one's skills up; by any standard this rating is a real handful. Add to the tasks of basic attitude instrument flying the complexity of operating the airplane and talking on the radio and dealing with navigational charts and so on, and you begin to see the difficulty. There is a reason all commercial airplanes of any size have two pilots for every operation.


(Here is a '70s jet panel. Notice that there is no turn coordinator, and the slip / skid ball is on the AI. Also, the navigation instruments are integrated tightly with the flight instruments.)

But there is a huge payoff for the effort and toil involved. It is these instruments, coupled with radio communication and radar-based Air Traffic Control, which enable an airplane to fly in anything less than good visual conditions with such great safety (and good visual conditions prevail in, at best, about 70% of the Lower 48 at any given time, and often much less). This is the system that lets you take off and immediately enter the clouds and not see the ground or anything else for four hours until you pop out of the clouds again 100' above the runway, perfectly aligned beneath you, at your destination. Absolutely, freakin', mind-blowingly cool when you think about it.

This is the world of the airline pilot, and it is quite different from that of the bush pilot. I love this system, and THIS is what is in my bone marrow as describing what a pilot is and does. We both control airplanes, but the similarities end there. I admire the bush pilot, but I wouldn't trade places.

5 comments:

matty said...

Fascinating. You know looking at all the panels it's pretty intimidating to think a pilot has all these lives at his fingertips just guiding through the skies with dials and instruments, instead of physically looking out the window to make sure the sky and horizon are aligned. Pretty fascinating and humbling too. You do this? Hot damn!

Anonymous said...

HUDs ruin cross checks. Heck I remember looking at the instrument layout of the T-37 Tweet (worth looking at...set up opposite of every civilian aircraft...they ignored things like human factors back in the early 50s) after being out of it for 6 months and wondering how I flew it. By that point I had been flying the T-1A (Beech 400) with its PFDs and whatnot. A HUD, however, totally kills your cross-check. I once could fly a PAR with nothing but those six instuments with no problem...or an ILS. I guess thats some of the ol stick and rudder airmanship we lose due to technology. Then again..is that a loss? We no longer have to manually tune ADFs/NDBs like they had to back in the day...and thats a good thing!

Anonymous said...

http://flightsim.com/review/tweet/ss109.jpg Here is a view that just about every AF pilot can appreciate...the left seat of the tweet. Note the very old school instrument setup...student pilots are still learning instruments in this jet. The instructor..who sat in the right seat...would fly off the students instruments. This is more than akward but has also been causal in more than a few accidents due to spacial-D. Just imagine flying down to mins while looking down and to the left!

wunelle said...

Matty: I think this was the single most amazing thing to me when I learned to fly, even moreso than the tangible magic of getting something heavier-than-air (seriously heavier in the case of something like my DC-8) aloft. Once one gets one's head wrapped around the miracle of controlled flight, it is, to me, the technology that makes it all possible in a practical way that occupies my mind. The cockpit of a modern large jet is an astounding conglomeration of systems and small motors and various machinery, all of which work in concert to enable a safe and uneventful flight (and if you knew the numbers of flight segments in the US on a given day, that safety record is stupefying).

Anon: I actually have very limited experience with a HUD, tho only in a training environment. When I flew the Dornier 328, our airplanes had come from Horizon, and they had HUDs installed in theirs. We took the HUDs out (since it considerably complicates pilot training), but the sim still had the equipment installed. It was a blast to fly, but yeah, I can see that one's scan would pretty much go away if you used it much. (Though let's be honest: with a flite director the scanning needs are much reduced anyway. I'd fear a true raw data non-precision approach nowadays).

And off the record, I'm a happy guy to never have to shoot an NDB approach again!

That pic looks like it came from a sim program!

Anonymous said...

That did come off a sim program....I could not find a real pic or a copy of a instrument poster that we used to use to "chairfly" our training missions.