Preventing against shedding

Nineteen elements, one station element, and a component board rather than a rig (our capital estimate).

1. Anti-ice and de-ice are not synonyms

This is the distinction candidates most often blur, and it decides how each system is operated and maintained.

Anti-ice prevents ice forming. It runs before and during the icing encounter — heated pitot tubes, heated windshields, hot air on a leading edge, chemical weeping systems. It must be on early, and a system switched on after ice has formed may not clear it.

De-ice removes ice that has already accumulated. Pneumatic boots are the classic: they inflate, crack the ice off, and deflate. They are used cyclically after a layer has built, and using them too early — on a thin layer — can push the ice into a shape the boot cannot then shed.

So the maintenance question differs too. An anti-ice system is judged on whether it produces enough heat, early enough; a de-ice system on whether it inflates fully, in sequence, and deflates cleanly.

K1 is why any of it matters: ice changes the shape of the wing. Not the weight primarily — the shape. A small amount of roughness on a leading edge can cost a large fraction of maximum lift and drop the stalling angle substantially, which is GEN-J Concepts §1's R2 in a different form.

2. Boots are rubber, and rubber is destroyed by the wrong things

S3, R3, K6.

A pneumatic boot is a bonded rubber structure, and the two things that ruin it are invisible until it fails:

• The wrong cleaner or solvent. Boots are cleaned with the manufacturer's approved product only. General shop solvents attack the rubber, and the damage shows as softening, swelling or cracking later (GEN-G Concepts §4).
• Over-inflation. Boots have a specified inflation pressure. Over-pressure stretches and eventually delaminates them.

A dressing is applied after cleaning where the manufacturer specifies one — it protects against ozone and ultraviolet, both of which age rubber whether or not the aircraft flies.

R3 extends the same idea to heated windshields, which are laminated assemblies with embedded elements: the wrong cleaner crazes the surface permanently (AF-B Concepts §7).

3. S4 is the cheapest test of an expensive assumption

Troubleshoot an electrically-heated pitot system is classified for simulator delivery, and it is one of a handful of such elements in the certificate.

Simulation is plausible here: the diagnosis is a simple circuit — supply, switch, element, ground — and the physical act is placing a probe (GEN-A Procedures Procedure 5).

Which is exactly why this element matters beyond itself. The program has ten simulator elements in landing gear and fuel that carry the largest apparatus decision in the plan (AF-E §7). If simulated troubleshooting works anywhere it works here, and if it fails here it will fail there — so this element is proposed as the early, cheap test, on a component board costing almost nothing.

For you as a candidate, the practical content is the same either way: a heated pitot that does not heat is a supply, a switch, an element or a ground, and voltage drop under load finds which.

4. Heated systems are electrical systems

S6, S7, and much of S1.

A heated windshield, a heated pitot and a heated stall warning vane are resistive loads, and they are diagnosed with the methods in GEN-A: predict the current, measure it, and use voltage drop under load to find resistance where there should be none.

They also draw significant current, which makes them a real load on the electrical system and a real fire risk if the protection is wrong (AF-K Concepts §4).

And an element that has partially failed still gets warm. It feels like it is working. Only a current measurement, against the expected value, tells you it is not.

5. What consumes this unit

License

CC BY-SA 4.0 (Licensing).