Part-66 Module 17: Propeller

The seven topics are laid out like a working life with a propeller: what one does, how one is built, the systems that act on it in flight, how it is maintained, and how it is put away. Read it that way and the table stops being a list of components and becomes the order you meet one in, from the air arriving at a blade to the grease on a hub in a store. Module 15 uses the same skeleton for the gas turbine, down to an opening row called Fundamentals and a closing pair of rows about the work rather than the theory.

Fundamentals and construction carry the physics. A propeller turns shaft torque into thrust by dragging a set of aerofoils through the air in a circle, and everything that describes one comes out of that picture: the angle each blade is set to, the gap between how far it should advance in one revolution and how far it actually does, and the efficiency that falls away as the tips get near the speed of sound. Construction is where the loads land. Blades of aluminium or composite carry a metal sheath along the leading edge against grit and rain, the hub holds each blade against a centrifugal pull far larger than the thrust that blade makes, and the vibration behaviour leaves some installations with an rpm range you are told not to sit in.

Pitch control is the largest system here and the one that reaches furthest outside the module. A turboprop is governed as one machine: the fuel control decides what the gas generator does, the governor decides blade angle, and between them they settle torque and rpm, so a propeller question turns into a Module 15 question more often than the syllabus admits. Beta range, ground fine, feather and reverse are positions along that same travel, and the question worth answering at each one is what holds the blade there, and what happens when the oil pressure goes away.

Synchronising and ice protection are the two smallest subjects, and neither one announces itself on a gauge. Two propellers turning at slightly different speeds make a beat you can hear and feel through the airframe, so a synchroniser trims one engine to match the other, and a synchrophaser goes further and holds a chosen phase between the blade sets. Ice earns a row of its own because it changes the aerofoil section, adds mass where it is least welcome and sheds unevenly, so electrically heated elements bonded to the leading edge fire in sequence rather than all together, and fluid systems fling glycol out along the blade from a slinger ring. The airframe’s own ice and rain protection belongs to Module 11, which goes a good deal deeper into it.

Maintenance and storage close the module, and they describe an ordinary week on the line. The work is blade tracking, static and dynamic balancing, a blade angle read at a reference station with a protractor, and nicks in the leading edge blended out within the limits the manufacturer allows, because a nick left alone is where a fatigue crack starts. Storage is the preservation that stops a steel hub and an aluminium blade corroding through a winter on the ground.

There are 32 questions and 40 minutes on the clock, and the count tells you less about Module 17 than it seems to. The seven topics describe one machine, not seven separate ones: a question filed under synchronising can’t be answered by anyone who doesn’t know what a governor does, and a construction question about counterweights is really a question about which way a blade wants to twist. Blade angle, the two speeds that decide it and the oil pressure that holds it are ideas a question can be built on from more than one row of the table.

You pass at 75%, which here means getting 24 right and having 8 in reserve, and because the rows describe one mechanism, the answers you get wrong are unlikely to be independent of each other. Hold blade angle and the forces on it the wrong way round and the same error surfaces under construction, under pitch control, under synchronising and again in the maintenance row, since each of those asks in some form what sets the angle and what holds it there. The reserve isn’t a pool of small separate risks; it rests on a handful of ideas, and any one of them can take several answers away with it.

It is one sitting whichever authority you are with: EASA splits a paper in two only when the clock is long, which in the B1.1 set means Modules 6, 7 and 11, and the assimilated UK text has no such provision at all. That suits the subject well enough: a paper answered in one pass rewards holding the whole mechanism in your head at once, which is how the syllabus was written and how it is easiest to carry in.

There is nothing to reconcile in this one: the two texts carry the same codes, the same titles word for word and the same knowledge level against every row, so the table below is really one syllabus with its level column printed twice. Read it for its shape instead: level 2 runs flat the whole way down until propeller maintenance, the single row set at level 3, which is the syllabus telling you that the part of this subject you will be trusted to act on is the part done with the aircraft in front of you.

No, and this is the only module of the thirteen where that answer holds row for row. Both give it 32 questions in 40 minutes, both divide the subject into seven topics numbered the same way, both word the titles identically, and both give every row the same knowledge level for category B1.1. The nine agreeing papers all match on the size of the examination; this is the one that keeps matching to the foot of the table, and there is nothing here to revise around.

The difference is the name on the paper: EASA calls it Module 17 and the UK CAA calls it Module 17A, and that letter is a fossil from an older text. Regulation (EU) 2023/989 abolished the A and B suffixes outright, so no Module 17A exists anywhere in the current EASA syllabus, which separates the categories by column instead. The UK adopted neither that amendment nor the one after it, so its Appendix I still holds the whole of the old module set, 17B included, with the B1.1 column pointing at 17A.

In practice this changes nothing about your revision, and it occasionally confuses your shopping. Course notes, textbooks and question banks are labelled inconsistently across the two regimes, and a book with 17A on the cover and a book with 17 on the cover describe the same seven rows in the same order. The thing worth checking isn’t the letter but whether the material was written for category B1.1, because the level each topic is examined at is read from that column and from no other.

The wider split between the two authorities is on the EASA versus UK CAA page: mutual recognition, which licence to go for, and what happened to the conversion route.

This page covers one of the 13 papers. The rest of the guide covers the route they sit inside: what the exam is, what else you must have done besides passing it, and how the two authorities differ.

Both authorities require the same thirteen subjects. Only the numbering and some of the titles differ, and the UK still uses the A suffix on four of them where EASA has dropped it. Each has a page of its own.