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Welcome to the CPL AGK question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.
Flightsurgeon created the topic: query in the exam
Respected all, there was one Question in the GK exam that I simply did not understand ( although I passed )
I cant recall exact but there was a question to check on the Magneto ground wire
it asked various options to either turn off the ignition, then testing the magnetos, or putting the engine on full RPM, or idle tne turning off the masters or the battery switch. There were various combinations of these. I couldnt really make sense of the wording and there were 5 options in contrast to the usual 4.
I know the mag check at 1700 and turning the mags left and right but I couldnt find anything in the books. Maybe Im not reading this carefully enough however, if anyone has thoughts I would be grateful
Checking the magneto for a 'dead cut' was once common practice but it seems to have lost favor in recent times.
The idea was to idle the engine just before shut-down then briefly turn the magnetos to 'off' and then back 'on' again. The idea was to observe a dead cut when the magnetos were turned 'off'.
If there was no dead cut it was an indication of a 'live magneto' that was likely to go undetected since the engine was eventually stopped by selecting idle cut-off with the mixture control. Selecting the mixture to idle cut-off ensures that the cylinders are left with no residual fuel.
It should be noted that an increasing number of RAA aircraft do not use magnetos, so the 'live magneto' problem does not exist.
Flightsurgeon replied the topic: query in the exam
Thank you Bob, unsure why CASA asked that question
Did I miss that detail in your book?
Maybe relevent for future students to know this point
Again it boils down to my age old quandry about a detailed syllabus
There is a summary on page 92 (old copy) in the CPL General Knowledge text book, which covers aspects of the magneto ignition system. Top of the list is that the magneto system is totally independent of the aircrafts electrical system, so the master switch will have no effect on magneto check. In fact if you have an electrical issue with the battery or alternator while flying, the engine will keep functioning.
You are correct about the magneto check at an RPM specified in the POH and selecting either L or R magneto. If there is no significant RPM drop, it means that the non-selected magneto is still functioning and not earthed. From a POH on line, the expected RPM drop is around 150 RPM. Note however that a greater RPM drop will be an indication of spark plug fowling.
If turning off the ignition leaves the engine running, is also an indication of a faulty earth, but you will not know which magneto is faulty, so not a correct answer.
CASA asks questions in this manner with several red herrings, to test your knowledge of the topic. In this case, master switch, battery switch which have no effect on the magnetos.
