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...

GPS & RAIM

It's common sense: make sure that your navigation equipment works before you fly. There are a few cases where this doesn't matter, like when you are flying locally using pilotage alone, but certainly if you are going to be flying at night, in the clouds, or over large bodies of water you want to know that the black boxes are telling you the right thing.

This is an old lesson. World War I ace and head of Eastern Air Lines Eddie Rickenbacker learned it the hard way, in 1942. This story comes from Seven Came Through, published by Doubleday in 1943.

It was the height of World War II, and Rickenbacker was on a secret mission to inspect all air combat groups. After a fact-finding tour of the European theatre, he headed to Hawai'i to begin inspection of the Pacific. His first destination was "1800 miles southwest" of Hawai'i; it was still wartime when the book was published, and Rickenbacker was a little coy about the destination. My best guess for the destination is Howland Island, which is famous because another prominent aviatrix, Amelia Earhart, never made it there, either.

The Army Air Corps assigned a B-17 and a crew to the flight, and they left Hickam Field in Honolulu on October 21, 1942. The departure didn't go well; a brake problem on the right main caused a groundloop.

Nobody was hurt, so the Army dug up another airplane and they launched again, crossing the ocean using dead reckoning and an octant. An octant works like a sextant, but uses one-eighth of a circle rather than one-sixth. The problem with dead reckoning over the ocean is that you can't determine drift or groundspeed, so you depend on the accuracy of the winds aloft forecast. We all know how that goes. But the octant and navigator were there for backup.

The octant had been loose on the navigation table aft of the cockpit during the groundloop, and had fallen. Damage from the fall made it inaccurate. With no way to find the destination island (whose direction finding equipment wasn't working), the B-17 eventually ditched. All eight made it into the rafts, but one crewmember died before they were rescued. Twenty one days later.

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Only a few luddites use celestial navigation in airplanes anymore. I've tried, but every time I go up the hill and take sights I end up knocking on my neighbor's door and asking when did you move to Montana? Where is the lesson for us?

In the USA, the Federal Aviation Regulations (14CFR) require regular checks of pitot-static (14CFR91.411) and VOR navigation systems (14CFR91.171). The magnetic compass should be checked with each annual inspection. We all know people who don't do the checks, and I can't tell you with a straight face that skipping a VOR check will make you spend 21 days in a raft.

Besides, I hear people say, nobody uses that stuff anyway. Now it's GPS, GPS, and when that fails GPS. How do you check the GPS?

First, let's get this out of the way: GPS can fail. Satellites have broken down. The military test jamming equipment. Incorrect almanacs have probably been uploaded. Ionospheric storms hit with shocking regularity and little or no warning. Antenna connections break. Voltage spikes fry avionics. Batteries leak in handhelds. The system is guaranteed to be 99.999% ("five nines") reliable, but there are 100,000 North Atlantic crossings every year, so statistically one of them will have GPS failure.

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What do we do about GPS failure?

The big expensive answer is WAAS, which I will leave to a future blog entry.

The simplest answer is that we cross check against other systems, usually pilotage and VOR/DME. (When I flew turboprops I carried WAC charts, partially for sightseeing and partially "just in case.")

The newest answer is you are required to check GPS integrity before every flight using RNAV (DPs, STARs, Q- and T-routes). This is called a RAIM check (Receiver Autonomous Integrity Monitoring). It requires at least five satellites (and barometric altimeter input). See this post for an explanation.

The requirement has always been there, but it was scattered through a lot of supplemental documents like TSOs and operating manuals. Now the FAA has clarified the requirement, in a new issue of Advisory Circular 90-100. They have even given you a website to help you do it. If worse comes to worse, you can get the information from Flight Service.

Even if it's not required for your operation, it sounds like a good idea.

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Modesty aside, I feel strongly enough about the study of the art of navigation that I wrote a book: Understanding Mathematics for Aircraft Navigation. Some people say that it contains more than pilots need to know. I've already said how I feel about that...