Altitude Engine and Manifold Pressure gauge

gkainz

gkainz

Final Approach
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Greg Kainz
We've had a little running email discussion within our club regarding our Dakota. One of our pilots said he believed the Manifold Pressure gauge had a momentary "inop" hiccup. I'm going to try to summarize the discussion so far and see what y'all have to say ... note: Pattern altitude in the note below is 6458'
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P1
- landing today - executed go-around Applied full power - went round. Turn base - power reduced - I look down @ MP gauge and it is not even registering 10 - it's about an inch below the 10 mark... The engine was still producing power - increased power, the MP gauge did not register. I was probably flying at 13-15"... turned final - still nothing... then had to land the plane... after landing & taxi MP gauge appeared to be reading normally.

I'm not sure how 'critical' the MP gauge issue is - it did come back on the ground.
-------------------------------
MO
Dakota MP gauge: A Manifold Pressure gauge is required (91.205) for each "altitude" engine. I have not previously noted the word "altitude" -- just assumed that each aircraft needs a MPG. What exactly is an "altitude engine"?

Anyway -- if it hasn't been fixed, I believe the plane should not be flown until this problem is solved.
--------------------------------
MO
correction: An "Altitude Engine" has equipment that allows it to maintain sea level manifold pressure as it climbs. (Turbo or other boost)

Altitude Engines must have Manifold Pressure gages. (An altitude engine is NOT a normally aspirated engine). That makes sense.

So: (Maybe) A manifold pressure gage is NOT required for our aircraft, according to my 2009 FAR/AIM, 91.205 b (8).

Anyone have a 2011 edition?

P2 quoted following from CFR14: 23

23.1305 Powerplant instruments.

(b) For reciprocating engine-powered airplanes. In addition to the powerplant instruments required by paragraph (a) of this section, the following powerplant instruments are required:
(5) A manifold pressure indicator for each altitude engine and for each engine with a controllable propeller.


Help me out here.
- Are we governed in some way by part 23?
- Is part 23 now part of the FAR/AIM?
- Has part 91 been modified to correspond with the above?

More: Folks who've flown after P1's note about MPG say it works normally.
-------------------------
 
gkainz said:
We've had a little running email discussion within our club regarding our Dakota. One of our pilots said he believed the Manifold Pressure gauge had a momentary "inop" hiccup. I'm going to try to summarize the discussion so far and see what y'all have to say ... note: Pattern altitude in the note below is 6458'
-------------------------------
P1
- landing today - executed go-around Applied full power - went round. Turn base - power reduced - I look down @ MP gauge and it is not even registering 10 - it's about an inch below the 10 mark... The engine was still producing power - increased power, the MP gauge did not register. I was probably flying at 13-15"... turned final - still nothing... then had to land the plane... after landing & taxi MP gauge appeared to be reading normally.

I'm not sure how 'critical' the MP gauge issue is - it did come back on the ground.
-------------------------------
MO
Dakota MP gauge: A Manifold Pressure gauge is required (91.205) for each "altitude" engine. I have not previously noted the word "altitude" -- just assumed that each aircraft needs a MPG. What exactly is an "altitude engine"?

Anyway -- if it hasn't been fixed, I believe the plane should not be flown until this problem is solved.
--------------------------------
MO
correction: An "Altitude Engine" has equipment that allows it to maintain sea level manifold pressure as it climbs. (Turbo or other boost)

Altitude Engines must have Manifold Pressure gages. (An altitude engine is NOT a normally aspirated engine). That makes sense.

So: (Maybe) A manifold pressure gage is NOT required for our aircraft, according to my 2009 FAR/AIM, 91.205 b (8).

Anyone have a 2011 edition?

P2 quoted following from CFR14: 23

23.1305 Powerplant instruments.

(b) For reciprocating engine-powered airplanes. In addition to the powerplant instruments required by paragraph (a) of this section, the following powerplant instruments are required:
(5) A manifold pressure indicator for each altitude engine and for each engine with a controllable propeller.


Help me out here.
- Are we governed in some way by part 23?
- Is part 23 now part of the FAR/AIM?
- Has part 91 been modified to correspond with the above?

More: Folks who've flown after P1's note about MPG say it works normally.
-------------------------
Click to expand...


First of all, Part 23 does not apply to your airplane. It was certified under CAR3. The CAR's apply.

BASIC EQUIPMENT
§ 3.655 Required basic equipment. The
following table shows the basic equipment items
required for type and airworthiness certification
of an airplane:
(a) Flight and navigational instruments.
(1) Air-speed indicator (see § 3.663).
(2) Altimeter.
(3) Magnetic direction indicator (see §
3.666)
(b) Power-plant instruments—(1) For each
engine or tank. (i) Fuel quantity indicator (see §
3.672).
(ii) Oil pressure indicator.
(iii) Oil temperature indicator.
(iv) Tachometer.
(2) For each engine or tank (if required in
reference section). (i) Carburetor air temperature
indicator (see § 3.676).
(ii) Coolant temperature indicator (if liquidcooled
engines used).
(iii) Cylinder head temperature indicator (see
§ 3.675).
(iv) Fuel pressure indicator (if pump-fed
engines used).
(v) Manifold pressure indicator (if altitude
engines used).
(vi) Oil quantity indicator (see § 3.674).
(c) Electrical equipment (if required by
reference section). (1) Master switch
arrangement (see § 3.688).
(2) Adequate source(s) of electrical energy
(see §§ 3.682 and 3.685).
(3) Electrical protective devices (see §
3.690).
(d) Miscellaneous equipment. (1)
Certificated safety belts for all occupants (see
Part 15 of this chapter).

14 CFR 1.1 Altitude engine means a reciprocating aircraft engine having a rated takeoff power that is producible from sea level to an established higher altitude.

Here is the TCDS for the airplane: http://rgl.faa.gov/Regulatory_and_G...90bd3d08b5d26e8625720a0054405a/$FILE/2A13.pdf
 
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If it has a constant speed propeller I believe the plane needs a manifold pressure gauge. How else are you gonna reconcile power numbers ?

Just a thought.........:idea:

Ben.
 
Anyone have any performance numbers written down accurate to 1" of MP for various flight regimes prior to P1?

Remember MP gauge is a suction gauge, really. It was saying that the engine was starved for air, indirectly. Could you have an air intake clogged, etc? Sucked a chunk of something up in there? How's the filter look?

There was an AD against Cessna 182s sucking chunks of the air box gasket into the carb. I don't know the Dakota's systems well enough to say, but I'd want to get the cowl off and look up the air intake, looking for loose doors, and also at the MP line for cracks, fittings loose, etc.

Is there an alternate air door triggered by suction on the Dakota if the main air intake is blocked by ice/etc? There's not on non-Turbo 182s, but I mention it because if there is you could be sucking non-filtered air through the box.

What was the Carb Heat setting before and during the go-around and during/after the landing? That's usually the method of getting unfiltered air on the 182 if the intake is clogged.

I don't think it can be "beyond the carb" since an induction system leak would show a high reading not lower.

Something made your gauge think there was really low pressure in your intake manifold, if the instrument itself isn't failing. Like sticking your hand over the end of a vacuum cleaner nozzle. The engine was "sucking hard" for air. But if you say the climb out power was normal, I'd suspect something wrong in the instrument itself. A leak in that MP line would go back to atmospheric pressure, just like if you were on the ground, which would be higher than 10" for sure!
 
N801BH said:
If it has a constant speed propeller I believe the plane needs a manifold pressure gauge.
Click to expand...
Per the regs R&W quoted, no, it doesn't, unless it has an "altitude engine," so only if a nonturbo c/s prop aircraft's equipment list or AFM says it's required would it be required, and I don't think a regular Dakota's equipment list or AFM says that.

How else are you gonna reconcile power numbers ?
Click to expand...
Well, you can't, but consider this a situation where rules and common sense aren't congruent.

Of course, if the MP gauge is inop, you'll have to go through the 91.213 procedures before you fly it again whether it's required or not -- the only question is whether you can fly with the MP gauge inop, and unless it's a Turbo Dakota, I believe the answer is yes. If so, it can be removed or deactivated/placarded, with the maintenance logged accordingly, and flown in that "properly altered condition acceptable to the Administrator."

Of course, if later pilots said it was working fine, maybe "P1" was wrong, and there's nothing to be done, but it's worth checking to be sure, and we'll leave the issue of whether or not they improperly flew an aircraft with an inop instrument for another discussion.

That said, there's nothing hard to find than an intermittent fault. I can't even begin to count the number of times I was assigned an aircraft in my military days where previous gripes were signed off "CND" ("could not duplicate") -- and that always bothered me.
 
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I flew it for 2 hrs after the original pilot (P1) and manifold pressure indicated normal in all phases of flight, including 5 take offs and landings. Normal takeoff MP indicated about 24" at 5860' @30.10 pressure that day (needle dances a bit at full power).

It's not a Turbo Dakota, just normally aspirated.

So, I wonder if picking up some debris (thinking like 'plastic grocery sack' or 'piece of paper' kind of debris) that could partially block the air intake and could make the gauge read low to nothing?

I don't know if P1 had carb heat selected or not - he didn't state in his email. Carb heat on is not a normal operation step in the Dakota.

If there were a crack, break or leak in the MP line, at complete failure, the gauge should have indicated ~23" (assuming ~7000' PA and 30.00 barometric pressure), correct? Refreshing myself with Deakin's "Manifold Pressure Sucks", without engine vacuum, Static Manifold Pressure should indicate atmospheric pressure minus 1" per 1000' above sea level.
 
Yes -- if the MP line was open, the MP goes to ambient (well, technically ambient plus any ram pressure in the engine compartment, but that ain't much) and stays there (BTDT). In any event, given P1 thought the MP was reading only a couple of inches lower than normal for that throttle position, and the situation could not be duplicated, I'd guess P1 just had the throttle back farther than he thought, and maybe excess speed was windmilling the prop so RPM was higher than normal for that throttle position.
 
I just went and re-read the description more carefully.

I originally thought it said P1 had already initiated the go-around and the gauge stayed at 10" AFTER the power was up.

I'm not reading it that way now. Ron's "a couple inches" caught my eye.

I was thinking there was a massive 10" discrepancy during my reply. Thus the "want to see the airbox" etc.

Sheesh. Sorry.
 
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