Someone Has to Read Them

The flight that was cancelled in the previous blog entry is back on again, but there's a new weather puzzle to solve. The scud is still present in the low terrain, but this time the air is stable, only trace icing expected. The clouds only go up to ten thousand, so I can climb through them and fly on top with no fancy routing. We'll cancel IFR and alerting after we get into uncontrolled airspace further north, so we can descend out of radio contact and look at the things that it's our job to look at, without people getting all antsy about us showing up to do an approach at our destination.

This time we do depart, and the flight goes as planned. The wings and windshield stay clean as we climb through the slowly brightening grey. I switch to sunglasses as we break through the top into the sunshine. I'm going northwest, and the sun has risen behind me, projecting a round rainbow on the clouds below me, visible through the propeller. It's called a glory or the glory of the pilot because you have to be between the sun and the clouds to see it. The colours repeat through the ring, faintly right into the centre and fading away to the outside. It's a light refraction effect, obviously, but according to the Wikipedia article it isn't certain how they are formed.

As we continue north, dark shadowy holes appear in the solid deck of clouds below, and then they widen to become green and grey and sparkling as the clouds scatter out and we can see the rocks and lakes and trees that define most of Canadian geography. the lakes are not yet frozen and some of the deciduous trees still have their coloured leaves. The clouds thin to occasional wisps and I cancel IFR to fly without having to follow a clearance or stay so far above terrain. Once we finish our work we turn again toward our destination. I'm listening to the Centre frequency as well as the air-to-air en route frequency of 126.7. I can't communicate with Centre, but I can hear other aircraft talking to them and pick up some information that way. A Dash-8 announces that they are in the missed approach from what we'll have to call Elk Creek. The fact that Elk Creek is below minima is a bad sign for the weather at my destination, because the two airports are relatively close, but then the Dash-8 pilot reads back a clearance to my destination. That's a good sign that overrides the bad one. He wouldn't miss and then go somewhere dubious. Sure enough I soon hear the Dash-8 pilot say he's planning the contact approach, which means he has the terrain in sight and is confident he'll remain visual all the way to the runway. He asks to fly direct a fix I'll call WIBEL and then I start to be able to hear the controller, who can't find WIBEL, even after the pilot spells it. The pilot tells him which approach it's on, and that it's the fix before AXFUG. (I wonder who makes these things up. It's kind of fun.) The controller says that the fix before AXFUG is WAGPO. I know what the problem is, but I can't interrupt their conversation. The two of them discuss this for a while, get the pilot an appropriate clearance, and then the controller has a number of calls to catch up on. When he's done I check in and add, "There's a NOTAM out today on the WIBEL/WAGPO situation." I knew I was planning in here VFR, but my eye ran over a NOTAM mentioning a waypoint substitution, and them repeating the waypoint name has triggered my recall.

The controller says, "Thanks, Aviatrix," using my real name over the frequency. He finds the NOTAM and reads it out. WAGPO has been temporarily replaced by WIBEL. It's curious that the airliner had a database that showed the new temporary waypoint while the controller didn't. I would have expected it to be the other way around, or to have them both be operating with post-its on their screens.

Photo Finish

I checked with maintenance regarding my recent post about the fire protection system. Our fire detector is photocell activated. The photocell is sensitive to a particular wavelength of light, supposedly characteristic of fire.

I didn't get to ask the obvious questions about why fire detection systems aren't overwhelmed with false positives from the sun, an awesome source of almost every electromagnetic wavelength, and able at some time of the day or some practical bank angle, to shine through every chink and opening in an engine cowling. An apprentice had a more pressing question about reinstallation of an exhaust manifold, and I was wearing silly girl shoes for a social event, so I teetered back out of the hangar to the office and left the maintenance to the maintainers.

Along with the answer to my question, and before the apprentice needed direction, I received the following story. A certain air carrier's night maintenance crew (they know who they are) conducted an inspection on at least one of the carrier's fleet. Their fire detection system used visible light, and the crew followed the manufacturer's instructions to test it by shining a flashlight on the detectors. The system failed the test. The crew was preparing to replace several thousand dollars worth of aviation grade electronic gear, when someone realized that that instructions were as old as the system, twenty years or so, and predated the invention of the LED flashlights the crew were using. The diodes were not emitting the necessary wavelength to trigger the detector, because when the instructions said "flashlight" an incandescent flashlight was assumed.

 The Wikipedia article on Fire Detection suggests that our photocell might be tuned to multiple wavelengths, possibly including UV and/or IR to compare the ratios. This still doesn't explain how an ordinary incandescent flashlight would trigger it, but the sun wouldn't, but does make the concept of photometric flame detection clearer. While looking for more information on flame detectors I discovered that there is a whole new generation of fire detection that uses machine intelligence to recognize the appearance of actual flames, something that is pretty fricking clear to humans. Combined with smoke detectors, something a commenter suggested on the previous post, there are enough different kinds of combustion detectors on aircraft to warrant a survey post on the topic, some time when my working day is shorter.

I was also entertained by the Wikipedia article on the Flashlight, which explains why Americans call them flashlights. The earliest zinc–carbon batteries could not provide a steady electric current so when combined with the inefficient carbon-filament bulbs, the result was a light that frequently blinked off so the battery could recover.

Digital Fuel Management

I've spent my career flying airplanes with instrument panels that haven't been substantially updated since the aircraft were designed in the 1950s or 1960s. Anything electronic is a newfangled after-market device not in the original aircraft specifications. Of course I haven't had any trouble using the newfangled stuff with which my various employers retrofit their aircraft. A new installation always comes with a manual, and you can usually find manufacturers' information online, too. I've enjoyed electronic tachs, EGTs, navcoms, and even a Sandel-OMFG-it's-everything-in-one-instrument, please don't let me push the button that makes it turn into a microwave oven just as I'm intercepting the glideslope (okay I had a little trouble with that one, but not as much trouble as the poor guy who owned it and had hired me to help him pass his IFR renewal with it). There's an instrument I've seen a few times, in airplanes I've flown once, or flown for short flights, and never bothered to learn how to use, but now there's one installed in an airplane I will fly for work, so I'd better learn to use it properly.

It's a Shadin Digital Fuel Management System, a fuel flow meter that, given information on how much fuel you started the flight with, should give excellent information on how much is left. See, normally you spend the flight comparing the known time and power setting with the fuel gauges and hoping everything you are looking at is as accurate as the agreement among them. You could have some weird fuel leak on the same day as you had a fuel gauge over-reading error and had your watch stop. It's not likely, but you could. That's the sort of not likely but it could happen scenario that pilots are paid to think about every day. The Shadin is another tool for tracking fuel consumption, and it's supposed to be extremely accurate, much better than fuel gauges, and it's digital, with readouts like fuel endurance so I don't have to peer at parallax, estimate needle widths, or even do any math.

Here's a post based on the manual for the Digiflo model, with notes on the slightly different Digidata model, which I think is on another member of the fleet. I start by verifying the fuel quantity the only way I really can, by visually confirming how much fuel is in the tanks. So this is on the ground, immediately after fuelling. Then I enter fuel on board into the device. It doesn't have a keyboard. In fact it's one of those nifty little pieces of electronics designed to fit in the dashboard hole made for a traditional round instrument, about the size of the bottom of a standard soup can. The picture below isn't quite the right product. Mine has three display windows, three push buttons, one three position toggle switch and a four position rotary knob. The top window normally displays whatever is selected by the rotary knob: NM/GAL, GAL. TO DESTINATION, GAL RESERVE or ENDURANCE HRS:MIN, and is flanked by the GAL REM. and GAL USED push buttons, which while held change the display appropriately. The bottom two windows display the fuel flow per engine.

The Digidata has the "ENTER/TEST" button in the left, a "REM/USED" toggle in the middle, a "FULL/ADD" toggle on the right, a rotary knob, and two display windows, one for the fuel flow and one for whatever is selected on the rotary knob. On that model, to display the fuel flow per engine you squeeze the REM/USED and FULL/ADD toggles together. I'm not sure if this is the right picture.

There are three options for entering fuel on board on the Digiflow. One is if I have filled all the tanks, in which case I move the FULL/ADD toggle to the FULL position and hold it there while pressing the ENTER/TEST button. I can then press the REM button to verify that it reads the full amount as fuel remaining. That's already set for the airplane. If I'm not filling the tanks I have to specify how much fuel I have added, by holding the REM button and pressing the TEST/ENTER button until it reaches the right level. For some reason there's a second way to do this, by holding the FUEL/ADD toggle in the ADD position and pressing the REM button to reach the right number. If I overshoot, I can press and hold the USED button and then press and hold the TEST/ENTER button until the right value is shown.

On the Digidata model I hold the REM/USED toggle in the REM position and hold down the ENTER/TEST button until the window displays the fuelled quantity. If I overshoot, I can remove some by holding the REM/USED toggle in the USED position and pressing the ENTER/TEST button to reduce the displayed quantity.

Once the amount is entered, I press the “ENTER/TEST” button and it should display in succession:

• 1. GOOd to verify that the display is OK
• 2. the K-factor (a calibration value for the fuel flow transducers)
• 3. the maximum usable fuel for the aircraft
• 4. software & revision version #
• 5. distance to a waypoint or destination

It achieves the fifth calculation because it can talk to--and I love this old meets new specification--the panel mount GPS or the LORAN C. Someone must have really loved his trusty LORAN C.

Fuel flow transducers are like little turbines spinning in the fuel lines, but if you thought "hmm, the speed of the turbine might not always be directly proportional to the fuel flow rate" then you would be right. If you not only did not pause to wonder that, but aren't sure whether it's worth pausing to wonder what it means, then you should pause instead to give thanks that there are engineers in the world, because it's important. The math to take into account the effect of 'viscous', 'transient' and 'turbulent' flows is probably fascinating. Maybe instead of stealing linguistics, I should have been stealing fluid dynamics. Those classes are probably harder to figure out when you drop in three quarters of the way through the semester, though. The manufacturer also assures us that if a transducer somehow gets stuck and stops spinning, it will not impede fuel flow to the engine.

The readout updates very rapidly and is easier to see than the EGT. I can see that once I get some familiarity with the airplane I will be setting mixtures by fuel flow, and then confirming that the EGT is within limits, rather than peering at the tiny digital or usually inaccurate analog EGT gauges. Also the display flashes if the fuel remaining is insufficient to reach the selected destination with 45 minutes reserve fuel.

En français:
un carburant - fuel
l'essence aviation (f) - aviation gasoline
le débit carburant - fuel flow
à court de carburant - low on fuel
avoir une panne d’essence - run out of fuel

Je veux apprendre à utiliser cet indicateur du débit carburant pour je n'ai jamais avoir une panne d'essence.

Happy Winter Holiday

This post is scheduled as the sun is directly overhead the Tropic of Capricorn, giving northerners like me the darkest day and the beginning of the return to longer days. No, I have no pagan upbringing. I like physics and I like understanding the model of the solar system that allows for a simple explanation of seasons, day length, and apparent solar and lunar positions. As far as I'm concerned, the reversing of the seasons is like the reversing of the Tonlé Sap river, an obvious reason to celebrate. Lots of people celebrate lots of things, about this time of year, and many of their festivals involve lights, probably influenced in timing if not in substance by the beginning of the end of the winter darkness.

I feel a little improper pronouncing to people what is in effect the blessing of a religion I don't strictly follow. Of course I do it sometimes, just as in Cambodia I gave many polite greetings and gestures that I didn't have the cultural or linguistic background to understand. I'm feel equally hypocritical wishing someone a happy Hanukkah or giving them Diwali greetings. I don't think there's anything wrong with doing so, nor in giving a religious greeting to someone who doesn't follow the corresponding faith. One Christian I know assured me that, despite the antics of some of his coreligionists, it is okay by him that not every joyous greeting or commercial activity in the entire month of December is labelled with the name of his God. In that vein, I will simply thank you all for reading, commenting, correcting, informing, and participating in what has turned into a quasi-community that I have the honour to host. I'm especially grateful to everyone who donated to the Cambodia effort, and I promise to continue telling you all about that next year.

I'll be back just before New Year's to see how I did on resolutions this year. I know already it's "badly," but a tradition is a tradition. It made me disproportionately happy when reader GPS Direct rolled off a list of silly and serious descriptors of me and admitted to knowing what my usual end-of-year topics would be. I think I didn't yet have "having people remember something about me" on my list of things that make me happy, but it should have been there. Thank you all for remembering my URL well enough to keep checking up on me for all this time.

In the meantime, enjoy anything you like to celebrate, and please keep an eye out for people for whom this is a season of pressure and loneliness. If you are someone who hopes only to survive this season, please hang on, and know that I at least am not expecting you to be automatically filled with joy and happiness just because of the date on the calendar, or the position of the sun with respect to the equator.