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ADI Sel Switch Ramp and Door Overspeed Inspection


Jay
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Okay gentleman. I've got two questions.

On the H-3 -1 preflight, the expanded portion of the AC inst. & eng. fuel control inverter check says to put the ADI sel switch in norm. Why?

Second question. I was reading through the -6, and for an overspeed of the ramp and door (150+KIAS), an inspection of the elevator and rudder surfaces and trim tabs are required. Why?

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I would assume (not being around H-3s) that the ADI selector switch has something to do with having the proper electrical load?

As for the ramp/door over speed; airflow is changed enough to possibly adversely affect the control surfaces on the empanage. (?)

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The ADI has two attitude references INS and a directional gyro. If the CoPilots Inverter is running it supplies the gyro and ADI with power (instead of the ESS AC) and the INS would also provide a reference and power to the ADI....two separate reference and power sources will display incorrectly and there is a potential to damage the ADI due to "parallel power sources"

As for the inspection I would have to agree it is due to the change in airflow...

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NATOPS1,

Thank you for the reply. I think I should have been more specific about the model. This is for an H3 that doesn't have a Co-pilot's inverter and is equipped with EFI's (Electronic Flight Instruments, glass ADI/HSI).

Again, this is for the AC Instrument and Engine Fuel Control Inverter check. Your response has been the instinctual response I've received from other engineers. But, after a bit of clarification, I can't seem to get a clear cut answer.

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As for the Norm postion on the ADI when running the CoPilots inverter from the DC postion, here is a pretty straight answer.

The ADI receives no positional guidance from the SCNS/INS when DC power source is selected. Worst case scenario, your in the WX and lose power to the ESS AC, you need to have the pilots select NORM instead of INS prior to changing the power source to DC, frequently if you switch the inverter while INS is selected the ADI will just roll and wobble. This is a really bad thing if your doing a instrument climb out.

Easy way to see it is (let the two cake eaters up front know first) while you are taxi'ing out and the pilots have INS selected, take the CO's inverter to the DC position and see what happens. I have never heard about ADI damage due to parallel power sources before, just the fact that the ADI will do goofy things with INS selected on DC power.

Dan

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OK, Now I'm confused on if you are talking about the Vert Ref switch (VG/INS) or the ADI Sel switch (NORM/SKE). They are two totally different things.

I don't see any reason for the ADI NORM/SKE switch to be in the NORM position for that Inverter check, since only the Vertical and Horizontal steering signals are affected by thet ADI switch.

Since I have never had the opportunity to work a new airplane like the H3, H2 or H2 1/2, so I don't know what all of them have for equipment, and believe it or not, the C130 T.O.s suck. I thought all H3 aircraft had dual INUs.

Edited by tinyclark
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H3s do have dual INUs, I haven't flown an H3 in almost 2 years but from what I remember they all had 2.

They didn't have duals when they first appeared. The FY92 H3s came with single INU. I think the FY93 H3s came with dual INU. I think the earlier models have since been retrofitted.

As to the ADI select switch I think it has something to do with attitude reference inputs. Been a while out of the plane now and without something to read I'm straining my memory.

For the overspeed inspections, a good point was made about the sloping longeron support for the high speed ramp aircraft. Unless it has to do with empennage twisting during an overspeed which is less on the aircraft with the enhanced sloping longerons.

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Dan Wilson,

I am not referring to the vertical reference switches.

I am referring to the ADI select switch (ADI, SKE Range, SKE positions)

I posed this question in the first place because I can't find a logical answer on my own. Let me clear up some confusion.

Here is the inverter check verbatim from the T.O. itself

*15. Inverter Checked

a. Place ADI SEL switches to NORM.

b. Place the voltage and frequency selector switch to the INV position.

c. Check the AC Inst and Engine Fuel Control inverter by placing

the phase selector switch to C phase and reading the voltage and frequency.

d. Turn AC Inst and Engine Fuel Control switch to the ESS AC/ESS AV position. The AC INV caution light should not illuminate. The frequency and voltage cannot be read from this position. Check TIT indicators for power indications.

e. On AF95-1001 and up, place the AC Inst and Engine Fuel Control Switch to the DC position.

I really hope this can clarify confusion so that there are no assumptions as to what I am asking.

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ADI Sel switch to Norm applies to H3's and H2 with EFIS (Glass flight instr), when in SKE it's giving different information to the EADI, it's hard to complete a preflight when the

ADI isn't displaying the proper information on the Autopilot check. Hope this clears some of this up.

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