Some Aircraft Questions, Mainly Related To Jets

  1. When should I be using anti ice? Right now I turn it on before taxi and turning off after landing. I’m sure it varies by airline. But what’s the general rule?

  2. Is FL260 the recommended time to switch to Mach from knots?

  3. Single engine taxing seems to be the norm from what I have gathered on recent flights. What dictates this and why?

  1. In what I fly, we don’t turn them on unless we’re actually going into clouds. But you’re right, it’ll depend on aircraft type, airline, SOP, etc.

  2. Don’t have a good answer for that.

  3. Saves fuel on longer taxis, especially if there are departure delays. Possibly engine time as well.

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Single engine taxi varies by airline as well and it’s not restricted to jets. Turboprops do it too. Q400s for example vary in their taxi procedure.

Don’t have answers for the others that vary above.

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So clouds are what causes the ice then? Or the moisture in the clouds…

Some one once told me KJFK requires it because pilots use to speed on the Taxiways. I told them you could speed with one engine also. I figured it was fuel related but the 6 months I worked as a Ramp Supervisor for JetBlue we had tons of APU issues. Im assuming the APU stays on until both engines are cranked so with that you are running your APUs longer, unless the APU stays on through take off.

Visible moisture, aka clouds, and temperture near 0C. I think it’s something like -20 to +5 is the range for temperature, though I could be wrong on that.

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Icing in aviation can happen for many reasons, even on warm days.

Here’s a decent pdf I hope this helps, maybe:


FWIW here is what we do from uncle airbus and company sops (A320)

  1. engine anti ice used on ground and in flight any time there is visible moisture and a TAT of 10 degrees C or less and a sat of -40deg c or greater. However descent will have engine anti ice on at any time in visible moisture even if SAT is below -40 degrees c

wing anti ice is inhibited on ground. If selected on, will run a 30second test before turning off until airborne. Used whilst flying any time visible ice accretion is seen on probe or wings.

  1. depends on environmental/performance factors. If you know your required climb mach, then set suitable indicated airspeed and transition when your airspeed matches required mach number. Mr airbus does this automatically.

  2. predominantly fuel saving.

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Note that there is a distinct different between anti-ice and de-ice. de-ice is usually isopropyl alcohol or some other fancy substance that is slung from the propellor blade route outwards to remove ice, then you have the de-ice boots, which are inflatable rubber/compound materials on the wing leading edge that can inflate to break the ice away, to consequently deflate again, some systems function on heat too, having the leading edge heated from the inside.

Anti-ice is all about prevention of ice-build up, this can be done by passive ways(coatings and other fancy chemicals) or more commonly bleed air from the engine.

Although, it’s usually approached as a singular thing, the distinction is not that important. One should also note that every aircraft and every airliner has a different set of guidelines, partially mandatory by the local regulators(thus included in the MMEL and TC/STC holder) and partially by the manufacturer. Then there’s some freedom and leeway on how to go about it.

As far as I know there is no general rule of thumb when it comes to anti-ice short of “make sure its on in icing conditions”.

  1. Mach number is based on a combination of the altimeter and IAS instrumentation, I dont think there is a set rule for changing to it but you can safely presume that if you can fly there without a pressure cabin then it’s safe to use the IAS.

3 fuel efficiency, besides engine running time means maintenance, if you need to fly between 2 bigger airports where you easily have a 20 minute taxi time then it’s nice to save 20 minutes on both engine(airport 1, engine 1, airport 2, engine 2). The engines on their own have sufficient energy to move the aircraft and it save FOD(Foreign Object Damage) being blown all around, it has happened before that severe damage was caused by a aircraft taxing with ever so slightly too much engine power.


For the planes I fly (light jets and turboprops), the pitot static anti-ice (it is not de-ice per se) goes on as we line up on the runway. We just recite a little mantra: ice, lights, ignitions, trims, flaps, autofeather, annunciator panel as we line up. (No autofeather for the Citations of course).

Once airborne, it just depends on the manufacturer or company SOP. The King Air the anti-ice such as the ice vanes, prop heat, and windshield heat go on at a reading of +5C and lower and in visible moisture…which basically means any clouds, precip, fog, or according to SimuFlite, visibility less than 1 mile. All of that stuff is technically ANTI-ice. Once in the ice, the generally accepted practice is to wait for a half to one inch of ice on the leading edges before cycling the DE-ice boots on the wings to pop it off. Limitation on the boot is to not pop it below -40C (or F) or you will likely crack or shred the boots (they become brittle at that temperature).

In the Citation - +10C or lower and visible moisture for the engine anti-ice, same limitation on the boots. The engine anti-ice brings on the heat for the first set of stators, and the first four or five feet of the heated leading edge. The rest of the wing is a boot (and the tail). We also have windshield heat valves on the Citation which are primarily used for anti-fogging, but can be used to anti-ice as well. And in a real pinch (I’ve never hit the switch in 20 years of flying them) - windshield alcohol can make a smear on the windscreen the width of your palm…LOL…

Mach to knots. It is usually up to ATC…they will query you or request an airspeed based on either indicated or Mach #…and it seems to differ when they do that. As for flying, I just use indicated until I transition to Mach based on the climb profile. In the Ultra it is 250 knots to .62 Mach, in the V it is 250 knots to .58 Mach. In the King Air it is…well…we try not to talk Mach in the King Air (as if the Citation isn’t embarrassing enough…)

Single engine taxi is popular with the airlines because it saves fuel. The Citation I fly is reluctant to taxi on one engine (it can), and the King Air simply won’t. At least, it won’t really from a dead stop. Also, both the types of planes I fly require you to turn the avionics off during an engine start to avoid spiking the sensitive electronics with current (something the airliners probably don’t have to do), which means you are without comms for that short period, and you probably have to re-initialize all your instrumentation data (V-speeds, FMS, other stuff)…so it is never worth shutting down an engine unless we are in the penalty box (holding for departure) for a long time (we never are - our patients don’t like that).



I just wanted to note that the Mach number is not a static thing for a set altitude, since it’s a combination between, IAS, airpressure and temperature, all of which are variables. What it does denote is a safe airspeed, if the mach number get’s too high you will start inducing a mach shock stall, where the air over the wing is going super sonic(this is usually the critical mach speed) and you start loosing lift on a conventional wing(well, any wing really). Once you push past this point you are transonic and quickly going for the sound barrier. once you have left the transsonic region(it’s before and after mach 1.) you need to push on a little more to experience a significant decrease in air resistance, at this point the aircraft will happily accelerate onwards with a reduced throttle, if your aircraft has supercruise.

In short, the physics get really interesting once you get in the higher mach region. This doesn’t really mean much for your average jet that flies somewhere between mach 0.7 and 0.9(really fancy ones that is), it’s still important to keep in mind how dangerous that corner of the flight regime is, even though it gets you there a lot faster, and cheaper then doing it in another way.


Depends a bit beach, but the airliners do suffer from the electronic spikes too, I know EMBRAER is sensitive to it and it wouldn’t surprise me much at all if many others do. There’s a reason we give them so many computers :wink:

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related question: Is the alcohol for the de-icing drinkable? :smiley:


Yeah, I wasn’t sure how all that works. I’m guessing that for some aircraft they can run the APU and have the electrical system totally isolated from the engine start circuitry. Man, I’d love to have an APU (for a lot of reasons). I still fly a slightly older King Air that requires you to turn off the running generator prior to starting the second engine or you’ll blow the current limiter (probably). After so many blown limiters, eventually Beechcraft (now Raytheon) developed a smart start circuit that now opens a relay to prevent that initial amperage surge from crossing into the main busses. So one of our King Airs is a smart circuit, the other is not. LOL…it never happens that someone forgets :wink:

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I’ll report back… :skull_crossbones:


LOL, I am asking because some of the alcohol used for cooling radar systems was indeed drinkable in the past.
Russians called it “plane vodka” according to Victor Belenko.

It’s usually made in a poisonous substance to avoid people drinking the fluids :stuck_out_tongue:

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Hmmm… I can’t imagine why… :wink: :smiley:

Haha, speaking of a hot bus :wink:

According to the MSDS its like 80-90% glycol… so I wouldn’t lol

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I’ve had a sip of german 90% spirits - burns a bit, but nothing too bad happens :stuck_out_tongue: