Cold Temperatures and Low Altitudes

[Note: I wrote the following for my EAA Chapter newsletter. Cold temperature altimeter errors scare me, since most of my flying is in a mountainous northern-tier state. And even if I have written about them before, everyone needs a reminder. So, here it is for everyone to read about.]

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We've all noticed that it's Winter, both by the calendar and by the thermometer. Or maybe, like me, you've had your annual furnace failure.

Pilots love winter flying. The cold, dense air makes both your engine and your wings stronger, and you can see forever because the air is so dry.

But the days are shorter, and that means more night flying. The night air is still cold and clear, and the lights shimmer brightly. You need to watch out for fog forming in the valleys, but that usually happens sometime after sunrise unless there's an inversion.

Now imagine yourself flying from Denver to southeast Idaho on a moonless night. Before you left you looked at a chart, whether online or paper, and noticed that the route takes you near Wyoming Peak, elevation 11,378' MSL. So you put on the oxygen and climbed to 12,500. Smart, right?

Well, let's see. Keep in mind that extreme temperatures distort your altimeter readings. Hot temperatures make the altimeter read low, while cold temperatures make the altimeter read high. "High to low, look out below."

People often forget that the altimeter error from cold temperatures increases with altitude. There's a table in the Aeronautical Information Manual (AIM), paragraph 7-2, that illustrates the problem. By the table, when the surface temperature is -20C (which is not all that cold for our winters), the altimeter error is 140 feet when you're 1000 feet above the surface, 280 feet when you're 2000 feet above, and 710 feet when you're 5000 feet above. It's worse when the surface temperature is colder.


Now let's get back to you cruising along at 12,500. You're comfortable in the dark, because your terrain display isn't showing any red. But does it know the surface temperature? What altitude does it use, anyway? Since you don't know, you get the Afton weather, either by tuning the ASOS or with the nifty XM receiver. "Afton Municipal Airport," it says. "0303 Zulu weather. Wind calm. Visibility 10. Sky clear below 12 thousand. Temperature -40 Celsius, dewpoint -42 Celsius, altimeter 3001..." You dutifully set the altimeter, thinking "It sure sounds cold down there!"

That high up, with the Afton temperature -40C, your altimeter error is about 1,000 feet! In other words, while your altimeter reads 12,500, your true altitude is closer to 11,500, putting you within 200 feet of the mountain. Which you can't see. Letting your altitude slip a little could ruin your night.

Pilots are generally carefully about hot conditions. We know to use the usual speeds for takeoff and landing, and to ignore that feeling that we're going too fast, because we're not. We know to allow more runway, too, and more room to climb. Perfect technique in hot conditions keeps you safe.

But perfect technique in cold conditions can kill you. You can pick a good altitude and hold it within an inch and still hit a mountain!

In Canada, Air Traffic Controllers automatically apply the correction to radar vectored altitudes, but in the US we ignore the problem. So, think about this when flying in or near the mountains on a cold night, or while IFR. Choose a higher altitude than you think you need, because in fact you need it. And this isn't just a Rockies thing: look at Mt. Marcy in the Adirondacks (5,344' MSL, nearly 4,000' above the nearest altimeter-setting source), or Mt. Washington in New Hampshire (6,288' MSL, more than 5,000' above the nearest source), or even North Carolina's Grandfather Mountain (5,960' MSL, about 3,000' above Boone, the nearest altimeter source). If there are mountains and winter (yes, even North Carolina has a winter; the ASOS at Boone is showing 01C with visibility 1/2 in snow) then there are cold temperature errors.

(Does anyone know what the situation is in Europe? Do controllers adjust altitudes for cold-temperatures, or do pilots have this information?)

See the AIM for more.

Starting off on the wrong foot

I'm confident that I will fly again, so I've started to review. Instrument flying really demands review, because the regulations are complex and changes happen quickly. (I've written about this before; see this post or this one.)

I found something interesting right away: a new departure procedure for Pocatello, pictured above. It's called the
KNURL ONE (OBSTACLE) departure.

A great way to improve your understanding of IFR flight, as well as your chart-reading skills, is to spend a lot of time asking "Why?" Why is there a new departure? Why does it use that radial? Why does it use that altitude? And the like.

The FAA uses two classes of departure procedure, SIDs (Standard Instrument Departures) and ODPs (Obstacle Departure Procedures). Wait, isn't the term SID deprecated? No; now it is undeprecated, or is that repricated, or maybe vindicated? Whatever you want to call it, see the preamble to the TAKEOFF MINIMUMS AND (OBSTACLE) DEPARTURE PROCEDURES section of any approach chart book. SIDs are back.

The first thing to notice is that it is an Obstacle Departure Procedure. The obvious clue is the word (OBSTACLE) in the procedure title, but there's a subtler clue as well, which is easy to miss because it is often, well, missing. SIDs generally do not include altitudes, and many that include altitudes use the notation (ATC) to indicate that the reason for the altitude restriction is for the convenience of Air Traffic Control; see for example the WHAMY ONE departure out of Portland, Oregon. You also see this with climb gradients, when ATC wants you to climb like crazy to get above the inbound traffic.

With IFR procedures the first consideration is altitude, so if you don't see one there's a reason. And ODPs, because of their nature, always include lots of altitudes. So, in the KNURL departure from runway 3, you read "Climb heading 028 to 5500, then..." That's to get you over the grain elevator.

After maneuvering away from the obstacles, the departure has you fly outbound on the PIH R-269 to KNURL, which is at 17DME. Ouch! That's a long way in a 172 or even an Archer, but it makes sense if you are headed west on V-500, which uses R-269. But that makes no sense in a 172 or Archer, since the MEA on V-500 between REAPS and DERSO is 17,000 MSL!

ODPs are optional and may be flown without a clearance, although I would consider it good form to inform ATC if you decide to fly it. So why would you follow an optional departure procedure that takes you down the radial you want to fly?

Worse, the ODP altitude is 7,500MSL. This leaves higher altitudes available for ATC, which is good. But it has you flying westbound at an eastbound VFR altitude, which would make me very uncomfortable on a marginal VFR day. If I had the equipment to get to 17,000 I would rather file for that altitude (or even higher) rather than fly head-to-head with the VFRs, nice folks though they are, down low.


Now let's look at how this DP fits with the enroute structure. There are six airways at Pocatello VOR, and because of terrain most departures are on one. Starting at north, V-21 goes northeast to Idaho Falls. Pocatello departures are unlikely to fly 17 miles west before turning northeast, especially since there is nothing to hit in that direction. Departing runway 21? Turning right at 400AGL will put you on the 016 radial? Departing runway 3? Just turn a little to the left. (Virtually no aircraft depart runways 17 or 35 except under extreme conditions, which would require some careful thought.)

The next airway is V-21 southeast bound. There is a crossing restriction at the VOR, so maybe a little jaunt down the 269 radial would be comforting. But all the way to KNURL? Plus, if you are on the ODP you are restricted to 7500, and the crossing altitude is 8000.

V-269 southeastbound follows the 235 radial, and the MEA is lower. If you're going that way, just fly V-269.

We've already discussed V-500.

V-269 northbound goes toward Salmon (LKT) over relatively low terrain for the first 50 miles. You are perfectly safe just turning to intercept, except perhaps departing runway 17. The same applies to V-257, toward DBS.

The other departure direction is toward Jackson Hole, WY. The heading is about 045, so one might be tempted to make a left turn departing runway 21, but that throws you toward high terrain. I always flew the right downwind departure, passing over the airport.

The conclusion?

Nobody will ever request the KNURL ODP!

It is still possible that ATC will assign the departure in order to get an airplane moving. Shoot the departure to 7500, keep the inbound at 9000, and everybody is happy. Once the departure is in radar contact they can vector it to where it wants to go. And if there's lost comm? Well, the departure is stuck down at 7500 for 10 minutes.

Still, you would interpret that as starting off on the wrong foot.

Testing Yourself

The doctor gave me a definitive diagnosis: it's Rheumatoid Arthritis. He said that it looked to him like my body would respond well to treatment, and he was right: every week I am a little stronger, and with rare exceptions I don't need to take anything for pain.

The recovery has an eery nick-of-time precision. And it's a good thing, too. First came the snow; I was strong enough to handle it, barely. It felt good to be outside working.

Friday night, my wife and I were watching a DVRed episode of Law and Order, one with an exquisitely complex plot. She had a glass of wine, but I was settling for the contact high, having given up alcohol because I am taking too many drugs that are hard on the liver. This was an easy decision, especially for a moderate drinker, about as easy as "no more winter IFR over the Cascades in singles." But that's another story.

An odd background noise caught my attention. Not a helicopter, not a truck, maybe something from the rail yard? No. A neighbor doing something? No, not at 11pm.

I went down to the basement. Is it the water softener? No. The noise was coming from the furnace.

I got some tools and started poking around, and pretty quickly decided that it was the exhaust blower fan. I fooled around with it, but the disassembly was more than I felt like tackling at 1am, and, besides, I didn't have any spare parts, so what was the point? We shut the whole thing down. We shut the furnace down. The night's predicted low was 20F.

But we have a backup or two. This is one of my big lessons to my flying students (I had to get to flying somehow, right?). I remembered the time I was shooting the GPS approach into Jackson Hole, WY [KJAC], night IMC. At that time, the GPS approach was an overlay for the VOR/DME approach, and I had written in the company training manual that in such cases, workload permitting, the pilot should set up both. Which I had. When the RAIM failure came, all I had to do was punch one button tand keep flying.

My wife and I got down to work lighting the fireplaces and the wood stove. I had turned off the gas to the gas fireplace, and went down to the garage to turn it back on. When I came back, she had stacked some half-split logs on the back porch. "I'm not too good at splitting these," she said.

They were way too big for either the fireplace or the wood stove. So I went out to split some logs. Being a good Yankee, I kept saying, "Best thing about a wood fiyah is that it wahms you twice!" Which it did. While I was outside I made note of a broken gutter, which I fixed this afternoon. If I recover much more I might put on a new roof or something.

The furnace guy came out in the morning and confirmed my blower fan diagnosis. He disassembled it, and found three broken impeller blades. We tried to run it with the missing blades, but the wheel was too imbalanced. Kind of like United 232, but way less deadly.

"We don't carry this part," he said, "We'll have to order it." So I went out to split some more logs. Not bad, considering that 6 weeks ago I couldn't erase the blackboard.

But we had some luck; he found a blower fan, and came back to install it. The furnace is running nicely, everyone is warm, and the bill is in the mail.

Still, it would have been nicer to fix it by pushing one button...

0.8

The students had finished today's exams, and I had a week to grade them...

My wife was back from Australia, so I didn't have to worry about the kids...

The METAR? 10SM CLR, but the weather was even better...

Besides, it was my birthday. So...

I went flying!

[Fine Print: since I do not have a medical certificate I had a friend with me who could act as Pilot-in-Command.]

It was just a proficiency run, nothing special. Steep turns (within ATP standards), an approach-to-landing stall, a little sighseeing to do a touch-and-go at an airport down the road, and then a couple of times around the pattern at home. I feel obliged to draw a pithy moral conclusion, the only one that comes to mind was that we had fun.

Why look for more?

Day 84

This was my 84th day on the ground, so let's focus on the future.

I am on our airport's General Aviation Improvement Committee, and it is so gratifying to see people working with the support of the powers that be to promote aviation. We are planning an Open House/Fly-In for late June, which is coming together nicely. We'll have a few warbirds on static display, and my club will have its planes cleaned up and ready ("YOU can fly this airplane!"). The local EAA Chapter will run a Young Eagles rally, giving airplane rides to kids [and, I should have a medical certificate by then, so I'll do some of the flying!]. Someone is working on military fly-bys, and someone else is working on a static display of a fire bomber, and someone else is working on the local regional carrier putting an RJ on display. People are getting fired up about flying.

I wish I had some nice slick LSA trainer to put on display. There's a big unfilled demand for Light Sport training in the area.

But that raises the question: where is flight instruction going? The November 30, 2009 issue of Aviation Week and Space Technology outlines the debate about training of professional pilots. Some feel, especially after last winter's Colgan Air icing accident, that regional pilots need more experience, and have proposed that new-hire first officers have an ATP certificate.

But Tim Brady, dean at Embry-Riddle's Daytona Beach campus, claims that this will force aspiring professional pilots to build time by instructing for 1,000 hours, "and repeating the same hour 1,000 times."

Brady was an Air Force pilot, so presumably never had the pleasure of 1,000 hours of instruction in singles and light twins (One might question whether lack of instructor experience qualifies one to head a campus devoted to flight training, but 40 years hanging around universities has taught me that there is no relationship between teaching experience or ability and administrative responsibilities.}

I have well over 1,000 hours of dual given, in everything from gliders to King Airs. Every hour is different. Those of you who are flight instructors (not just holders of instructor certificates) know what I mean. Here are a few of my every-one-is-different hours. Students have turned a routine stall demonstration into a spin. Instrument students have lost control in IMC. Students have keyed the mic to say something that should not have been said. They have lowered the landing gear early in icing conditions, and flown the ILS at cruise speed, trying to lower the gear while flying 30 knots faster than the maximum gear speed. They have achieved faster-than-gravity descent rates trying to catch the glideslope from above. Glider students have forgotten to turn right at tow release, leading to an up-close look at the towplane. That's a lot of recoveries and preventions.

Brady claims that ERAU students learn airline-style procedures from day one. This means SOPs, things like "At Skyburst Airlines, after an engine failure we climb to 400AGL without touching anything," or "At Aluminum Air we use QFE," or, most important of all, "Payday is Friday and we contribute 1% to your 401K." New-hires have successfully learned this stuff in three week ground school courses since the time of E. K. Gann.

What airline pilots are not learning is what to do when all of the screens go black. There have been more and more incidents like this lately. In 2008, two separate QANTAS A330s had dangerous uncommanded pitch changes after air data system anomalies. Air France 447 crashed into the Atlantic last summer, sending ACARS reports of airspeed problems. The captain of Colgan 3407 pulled back when there were stall indications. Nor are these accidents a new trend. Birgen Air lost a 757 in 1996 when the static ports were taped over; the crew couldn't handle the spurious airspeed indications. Northwest lost a 727 in 1974 due to pitot icing. These accidents led to hundreds - hundreds! - of passenger deaths.

Thinking about these accidents convinces me: when the screens go dark while I'm in back, I want the folks up front to have spent 1,000 hours in an underpowered aircraft with an airspeed indicator too far away to read and an unpredictable student at the controls. I'd like my crew to have crossed the Donner Pass in a 65hp Taylorcraft (Horrors! VFR!?!) or something like that. Four years in a simulator reading checklists isn't reading 1,000 checklists, it's reading the same checklist 1,000 times.