Navigation

I'm working with a commercial pilot candidate for the first time in quite a while, and the process is raising some interesting questions. The flying part hasn't changed much in the past 75 years or so, but in the USA commercial pilots candidates are required to have two hours each of day and night cross-country (navigation) training.

And I don't know what to teach him.

When confused about how to proceed there's often an axiom that starts things moving in the right direction. For commercial pilots, the axiom is "planning - anticipation - orientation -- efficiency." The commercial maneuvers themselves (steep turns, lazy 8s, chandelles, etc) are really just a vehicle for a pilot to plan and execute a complicated series of tasks. Many other tasks might do.

And so the goal of commercial navigation training must be to give the pilot practice planning and executing a complicated series of (navigational) tasks.

The rise of database navigation has been a true paradigm shift. (What most call GPS navigation and a few call RNAV is really database navigation: it's less important to know how the unit determined your position than it is to know that it has a database of fixes and elevations and procedures.)

So database navigation has to be part of the curriculum. It's very likely that his handheld has an expired database (truth to tell, my handheld has an expired database), so it is extra important to carry current charts. This used to mean a subscription to paper charts, but now the various iPad apps make it really easy to have current charts.

Route planning fits the axiom. An acceptable daytime route may be unacceptable when it's dark. Day or night, choose alternatives along the way, and beyond. Always plan the fuel realistically; for example, if anti-ice requires more fuel, you plan on using anti-ice the whole way. Know or anticipate what controllers will do, especially in airplanes whose fuel burn depends on altitude.

He needs to know how to program the route he chose (how do you get a lat/long into your handheld?), and how to reprogram a route. It would be nice if he knew what RAIM is, but this is VFR flying so there is no real requirement. I'll mention it, but only provide details if he asks.

The textbooks (unless there is one that I have yet to see) still include a lot of E6B problems. I don't think the need to adjust for the wind is going to disappear anytime soon, although GPS track and groundspeed make it much easier to find the proper wind-correction angle. But even without GPS, I am finding less and less use for the E6B. Since I don't fly high altitudes anymore, I don't need it to figure True Air Speed. But I also don't need it to figure wind correction angles: all of my E6B calculations have been replaced by the Rule of 60, an interesting little bit of mathematics that few pilots know even though the FAA requires it for every knowledge test except maybe parachute rigger.

The Rule of 60 says that if you are off-course by 1 degree then after 60 miles you will be 1 mile off course. This is a proportion, so after 30 miles you'd be half a mile off, and after 120 miles you'd be 2 miles off. The proportion still works for "small" angles, so after 60 miles with a 2 degree error, you're 2 miles off course, and with a 3 degree error you'd be 3 miles off.

(For the math nerds out there, the reason is that the sine of a small angle is approximately the angle, when the angle is measured in radians. One radian is about 60 degrees, so 1 degree is 1/60 of a radian. 'Nuff said.)

So when there's a 20 knot wind 15 degrees off the bow in our 140 knot Cherokee Six, the crosswind component is about 5 knots (20*(15/60)), the wind correction is about (5/140)*60, or 2 degrees, and the groundspeed is a little over 120. Close enough.

He needs to plan his descent carefully to avoid shock-cooling the engine, and to anticipate what pattern entry will work. This means knowing the forecast winds, and knowing the NOTAMs about runway closures. Runway slope or obstacles might be an issue, so the Airport/Facility Directory is a must (Have you noticed that the Electronic Flight Bags have resurrected the A/FD as the primary source of airport information?).

Departing from a strange airport means reviewing terrain, slope, SIDs and DPs, and the like.

I think he's going to be busy...

Which Way?

One of my mottos is "Sometimes you just have to fly toward the blue sky," and I have taken some monster diversions in my time. This post from UpShip! showing Airship Ventures's Zeppelin doing the same is a good reminder. You can check the flight track here.

Enjoy the closeup of the panel and the unusual instruments and terminology. Did you know that you can get training in airship flying from these folks? It's a bit too pricey for me right now, but someday...

LORAN

I already commented on the decommissioning of LORAN-C at N631S. In addition, here are two excerpts from my book, Understanding Mathematics for Aircraft Navigation.


p. xiv [A World War II story from my father]: "...enroute to tiny Eniwetok, they were unable to make celestial sights due to weather. He and another officer decided to try the ship's LORAN. The LORAN worked and gave them an indication of their position, but the captain refused to believe it."


p. 168 "[they] might have been more successful if they had used the LORAN in their daily navigational chores, rather than waiting until a crisis. The accumulated experience might have tempered the captain's skepticism. Conversely, older methods that aren't used at every opportunity become rusty and unreliable, especially in an emergency."

Someone once noted that a large number of navigators have been replaced by a small number of engineers. The engineers have made our navigational lives immeasurably easier. But shit happens, so it is important to practice the basics. I don't mean that you have to torture yourself and turn off all of your avionics; looking at a chart and keeping a navigation log keeps your dead reckoning and piloting skills current.



Instead of playing my "old man" card and bemoaning the decommissioning of the last CONSOLAN station within my lifetime (it was on Nantucket), here's something more positive, an essay from the National Air & Space Museum blog on the remnants of the lighted airway system, and some chart scans that show the beacons. I'm ashamed to say that I have never navigated by these beacons, despite a lot of Montana flying. I missed out on the four-course range and CONSOLAN and DECCA and OMEGA-VLF, so I should get myself back up there and see for myself.


Of course I want LORAN to stay, even if it goes, remember:
back yourself up; fly safely!

Will We All Get Sick?

This is not about swine flu, or even type A(H1N1) flu. It's about airplanes.

I love navigation, every aspect of it. I have taught courses, I have done research, I even wrote a book about it. Navigation strikes the perfect balance between action and contemplation. I like to think that I have explored every corner of the subject, but this week I learned something new.

One of my instrument students is working on adding to his cross-country time. He needed to pick up a friend at an airport a couple of hundred miles away. I helped him with some flight planning, but the morning of the trip the weather was less than perfect VFR. Of course I would be happy to come along, I said. We spent some time going over my interpretation of the weather; it was important for him to understand why I thought it was safe.

My motives were a little less than pure. I am thinking about upgrading my handheld GPS, and he owns one of the ones I am considering. I figured that it was a good chance to play with the unit in anger.

The trip out was rough. There were scattered snow showers. Some were light enough to fly through, but some were not, and we had to divert a few times.

But the turbulence was worse than the snow. "Continuous light and occasional moderate, and I mean continuous, every inch of the way," was how I put it to Flight Watch. (For those of you overseas, Flight Watch is actually Enroute Weather Advisory Service; and an inch is about 2.54cm.)

"He's gonna get sick," was how my student put it, referring to his friend.

And he was right. The climbout was rough, and it stayed rough, just a little smoother than before. I went on playing with the GPS and pointing things out on the charts, both IFR and VFR, and keeping a flight log, and playing with the camera on my iPhone. I even took out my circular E6-B and figured a new ETA when the headwind proved a little stronger than anticipated. I dug out the printed weather briefing and pointed out that the winds aloft were forecast to decrease as we got closer to home. It was a fine afternoon for flying, and for satisfying someone's curiosity about how to do longer cross-countries in more conditions.

But it got quiet in back. Pretty soon I heard the headsets fumble in the intercom, and then I heard the sound of a bag in use.

I pointed an air vent to keep the smell away and went on with my business. My student wanted to try something on the GPS, but was having trouble holding heading and altitude while he was distracted. I offered to take the flight controls. I like to think I fly smoothly, even when it's rough.

"Oops, that was a mistake," he said.

"Do you want the controls back?"

"Oh, yes, please." Being at the controls helps keep the stomach under control.

So while he stared out the window I did all the navigating. I thought I was fine, but let's just say that after we landed I didn't feel like eating for a while.

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The big lesson was about the physiology of being a navigator. Navigating is pretty easy these days; we don't follow in the footsteps of navigator Riiser-Larsen on Amundsen's expedition to the North Pole in the airship Norge (that's a hard 'g', by the way). Unable to take a sextant sight from the control car, Riiser-Larsen climbed to to the top and took the sextant sight in -40 degree air at 60 knots indicated. Ouch! And we don't have to do the calculations anymore. Most people find that a real advantage.

But think about the poor navigator in, say, a DC-3 or DC-4 or even B-52. He's the second most nerdy guy on the crew (the radio operator being the nerdiest). He sits and does his calculations at a chart table, far from center of gravity. When it's rough, he really gets tossed around. But he doesn't get sick! (We'll omit the part about enjoying the trigonometry calculations; we all know pilots don't go for that.)

Lots of pilots get sick. Gordon Baxter wrote about it in his columns for Flying. Many glider pilots spend their first flight or two of the season in absolute agony, returning with filled gallon zipper-lock bags.

One afternoon, two of use were headed home empty in a Cessna 414. We were both coming up on recurrent training, and I, as the instructor, got the bright idea that we should dig out the POH and quiz each other on the airplane systems. After a couple of minutes of reading questions to me, Al closed the book and said "That's it." He stared straight ahead. I gave the controls to him and read about systems until it was time to start down.

So, let's all have a little respect for the navigator. He's the nerdy guy with the iron stomach. Aviation would never have gotten anywhere without him.

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...