Friday, November 11, 2011

Diversion, Conversion

Cruising along at 5,500 feet, en route to the Columbia airport, my student had good reason to believe he’d never get there. Sure enough, in preparation for his upcoming private pilot check ride, I asked him divert to another airport. He began circling over a chosen landmark, produced a VFR chart, drew a course line, estimated the heading, distance, time, and fuel required to the new airport, all the while maintaing altitude and looking for traffic. His juggling of these priorities was impressive, but he soon discovered that his chart had been folded so many times that the frequencies for the new destination airport had been rendered illegible. Flustered, he scrambled to locate his Airport/Facility Directory while I kept an eye out for traffic and mused about how many times a day pilots must now be asking their instructors “Is it okay for me to use my iPad?”

I’ve logged nearly 1200 hours since my first flight with the iPad 1 and frankly, I’ve never looked back. When I was still searching for the ideal EFB back in 2009, I explained how the FAA doesn’t require any certification or qualification for EFBs under most Part 91 operations. Just recently, the FAA’s own Safety Briefing publication had yet another article making the same observations. Given that pilots are adopting EFBs faster than you can say “decommissioned NDB,” it’s time for instructors to start making EFBs part of the training they offer as well as part of their own training. I tell student pilots I train “Go ahead and use an iPad if you want, but be prepared with a credible back-up strategy in case your iPad fails or your instructor decides to simulate a failure.”


Before you start gnashing your teeth, complaining about newfangled gadgets, and pining for the good old days of slide rules, cigarettes smoking in the cockpit, and navigating via A-N Range, consider that combining old techniques with new approaches can actually aid in teaching pilots to that elusive correlative level of knowledge. The key concept here is combining approaches, not rejecting one in favor of the other. Here’s an overview of the old school approach, followed by some mash-ups of familiar approaches with new tools and software.

Old School Planning

The first half dozen times through the cross-country flight planning process, I like student pilots to do navigation calculations manually so they’ll understand and appreciate what their EFB or flight planning software will eventually be doing for them. My favorite nav log form is available for free from Dauntless-Software. The two basic variations in nav logs involve whether the True Course (TC) is first corrected for magnetic variation or for the wind correction angle.





ATC uses and refers to magnetic directions, so I say cut to the chase and go magnetic. Winds aloft forecasts are provided with true directions, so you'll need to account for that if you choose the TC-VAR-MC-WCA-MH format.

Virtually all nav logs end up with a Compass Heading (CH), to which I say “Who cares?” If you always set your aircraft's heading indicator using the compass correction card, calculating a CH is simply gilding the lily. If your aircraft doesn't have a heading indicator, then by all means compute the CH until such time as you manage to catch up with the later half of 20th century aviation technology.

I teach students to complete a paper nav log in this general sequence.

  1. Calculate climb performance and ground speed
  2. Determine the location of the Top-of-Climb (TOC)
  3. Calculate cruise performance and ground speed
  4. Determine the location of the Time-of-Descent (TOD).
  5. Divide the course between the TOC and TOD into legs of equal length.
Aircraft consume more fuel and have a slower ground speed during the climb to altitude, so calculating where you'll reach the top-of-climb (TOC) is important. And if you want to avoid arriving high and hot, the time-of-descent is something you’ll want to plan for. Want to use an electronic E6B instead of a slide rule to do these calculations? Fine by me.

With TOC and TOD marked on your chart, try dividing the remaining course into legs of equal length. Sometimes this works, sometimes there aren’t good landmarks. If defining equal leg distances does work, you only need to calculate time, fuel, and distance for one leg to have the numbers for the other legs. Choosing landmarks on a paper chart is the ultimate in flexibility: You can choose whatever you want. With an EFB or internet-based planner, waypoints selection is as simple.

High-Tech Planning

The sad fact is we're well into the second millennium and there aren’t many computerized flight planners that account for the time- or fuel-to-climb. A few internet-based planners that do (to varying degrees) include DUAT (not to be confused with DUATS), AOPA’s Flight Planner, and FlightAware.

Once you’ve entered a profile for your aircraft, the DUAT flight planner will provide the location TOC and TOD in latitude/longitude format. Not terribly handy, but it also provides a magnetic course and distance which does turn out to be useful. More on that later.


The browser-based flight planners from AOPA and FlightAware both account for fuel consumed in the climb and descent, but they don’t tell you where TOC and TOD are located. Bummer about that.


FlightAware’s planner adds some value by including the estimated fuel costs for various altitudes, winds aloft forecast, and routes. In this example you can see that you’d only save a few bucks by climbing to 11,000 feet versus 9,000 feet. To access FlightAware’s flight planning features, you’ll need to set up an account. Don’t worry, it’s a free and simple process. Be advised that FlightAware’s planner doesn’t work completely on the iPad browsers I’ve tried.



So what about specifying waypoints that aren’t pre-defined objects like airports, VORs or airway intersections? Most planners allow you to enter your own waypoints as Lat/Long coordinates or as a VOR-radial-distance. That’s not terribly user-friendly, but it works.
You can add custom checkpoints in ForeFlight’s map view by tapping on the map view. A dialog will appear allowing you to add the location as a user-defined coordinate. If you tap on your course line, it’s easy to inadvertently change the course slightly and you won’t know the leg distance until you’ve tapped, but there you go.

If you know the lat/long for a waypoint, you can enter that into a ForeFlight route. Below, the lat/long that DUAT calculated for TOC has been entered as a TOC waypoint.



If you know the distance and radial from a VOR, you can enter a waypoint in ForeFlight using theta/rho format: VOR_id/radial/distance. This approach also works with airport identifiers. Below, I’ve taken the TOC and TOD data from the DUAT flight planner output and entered them as waypoints in the format KOAK/133/16 and KSBA/315/29.



Nav Log in Action

Using a paper nav log in flight starts with recording your departure time. For short trips, just record the two-digit minutes after the hour. Then to calculate estimated time of arrival (ETA) for the next checkpoint, add the time your off time to the estimated time en route (ETE) for the first checkpoint. When you reach the checkpoint, record the actual time of arrival (ATA), add that to the next ETE and you have the ETA for the next checkpoint. If your ETA calculations consistently differ from the ATA, consider doing an winds aloft and TAS calculation.

ForeFlight kinda-sorta follows the paper nav log tradition, but the assumption is that ForeFlight will use GPS information to calculate your estimated time en route for each leg in real-time based on your current ground speed. I find ForeFlight’s nav log display a bit cumbersome and difficult to read in flight, but that could be due to my 50-something eyesight. If you want a historical record, why not combine a paper nav log with your EFB?

Electronic Diversion

Planning an in-flight diversion with an app like ForeFlight is the height of simplicity.

  1. Tap and hold on the airport to which you wish to divert
  2. A dialog will appear showing the known waypoints in the area
  3. Tap on the orange D-> button for the selection you 



EFBs can provide real-time calculation of the desired track, ETE, and fuel consumed, but you can do the same sort of thing with many panel mounted GPS. Electronic diversions are so easy and with no plotter, pencil and calculator to juggle, it's no wonder some pilots feel they are cheating. Hand-calculated diversions can be just as dangerous as fixating on pretty colors on a moving map. Having a quick way to calculate a diversion in real life gives you more time to look outside for traffic and manage whatever emergency or urgent situation you're facing. That seems like a good thing, not the work of the devil.

Combine and Conquer

Whether it be in paper format, electronic format, or a combination of the two, preparing and using a nav log in flight can be a curiously satisfying experience. Teaching student pilots the old ways is still a valuable part of the aviation education equation, but introducing and integrating new tools doesn't need to detract from the experience. High tech solutions can enhance accuracy and safety. As with anything in aviation, understanding the limitations of technology is a more productive approach that rejecting new techniques out-of-hand. To my mind, if a pilot can learn the basics and then combine old school and way cool, that strikes at the heart of the vaunted correlative level of knowledge.

3 comments:

brec said...

No mention of fltplan.com? No TOC or TOD, but climb fuel is accounted for.

John Ewing said...

FltPlan is a pretty good service, though the UI is a bit weird until you get used to it. Also, their target user group seems to be charter pilots flying under IFR rather than the average GA pilot.

Ron said...

I never have students physically writing out all that stuff during a diversion. You're right, it's dangerous to have their heads down in the cockpit any more than absolutely necessary.

I teach them to use simple rules-of-thumb to estimate time, fuel, and distance. It's easy to set power for around 120 knots (2 nm/min), burn around 10 gph (1 gal/6 min), and they can estimate distance on a chart fairly accurately by just looking at it once they're taught how.

I don't think the lack of a heading indicator means they're a luddite. It might mean they're a very smart pilot and are learning in a Citabria, Cub, Champ, Decathlon, Husky, or one of a dozen other tailwheel airplanes. :)

Having said that, I take the same attitude you do toward iPads and other such devices. Use them intelligently, but ensure you have a Plan B if they fail or are failed by the DPE.