JAR questions
 

Hello folks

I am doing my ATPL exams now and on my last sitting there were 2 questions that I cann´t find the anserws to in my textbooks.

1. Why are there 2 trim knobs on some control wheels?

2. What do passengers breath through their masks?
The anserws for this on were like
a) 100% oxygen
b) oxygen + cabin air
c) cabin air

any help would be great.

Jonasraf

I'm not sure about the answer to your first question, maybe its for redundancy?

For the second question the answer I believe is Oxygen plus cabin air. I remember something about them useless in a smoky environment as they use a mixture of the chemically produced oxygen and cabin air.

I am, as always, happy to stand corrected.

Cheers

TBL:D

1.as a precaution to help prevent trim runaway!

2.100% oxygen from a chemical mixture cant remember the exact substance but its that!No oxygen comes from the mask until the fuse is broke which allows the 2 substances to connect and form a chemical reaction causin 100% oxygen.


Now when does the Bow Wave APPEAR?

1. there are 2 trim devices so as to prevent trim runaway (i'm assuming that you are refering to the 2 switches on the control yoke and not the actual wheels either side of the throttle quadrant)

2. The passenger oxgen system consists of a chemical oxygen generator containing a sodium chlorate charge block. When the mask is pulled a reaction is started which produces pure oxygen. This is mixed with cabin air (possibly to cool it from the exothermic reaction). This makes it usless in a smoke filled cabin.

Re. the two trim switches - not really to prevent trim RUNAWAY, but to prevent inadvertent trim operation. One of each pair of switches is an ARMING switch and the other is the DIRECTION selector. Therefore, in order to activate any trim, BOTH switches have to be operated. An interesting party trick is to operate the trim switches in opposite directions ... Q? What will happen?
A. the trim operates in the sense commanded by the DIRECTION switch, since the ARMING switch works the same in either sense.

Just want to say thank you all for your help.

:D :D

Question 2. - Nothing to add

Question 1. - Split Switch

In light A/C you will find usually either a cut-off switch or CB easily accessible or the mentioned split switch.

In the split switch - if you look at the electric wiring diagrams you usually see that one part activates the trim motor while the second part activates the clutch to the trim wheel. This, as you mentioned to avoid trim runaway. If any one of the switches would fuse together the contacts or shorten in any other way the missing input from the second switch would avoid the runaway.

The AFM usually explains that.

On some A/C you check this when checking the Autopilot e.g. PIPER SENECA III. Push only the left part of the trim switch forward or rearwards and try the manual trim wheel. No difference to manual operation should result. Try the same with the right part of the switch you should note that you need more force to turn the trim wheel because the clutch is now closed and you also turn the electric motor. (Derived from Piper Seneca III Information Manual Section 9 Supplement 8 for PA-34-220T)

CAUTION: No liability or any responsibility can be derived from this tip in any circumstance. Only the official source such as AFM/AOM shall be used to perform such check.