Diagnose this ...

[old man emu]

19 minutes ago, Yenn said:

I know what happened, do you? I will fix it before next flight.

That's because you know your aircraft systems and basically how things work.

 

 

I think that the simplest cause is a bad electrical connection. I would check the winding around the spark plug lead and the connection to ground. Nice compact little tacho. I might get one for my bike.

 

 

[Blueadventures]

31 minutes ago, old man emu said:

No. What I was after was for people to go back to basics and work out, from their knowledge of AIRCRAFT SYSTEMS, what could have been the cause.

You can't tell me that when you go flying and conditions are really nice that you don't relax and watch the world go by? Or are all flights spent in fear of structural, mechanical failure or dramatic changes in "weather" that you are required to spend the whole flight assiduously gazing at your instrument panel? 

 

 

 Thanks Yenn. That was the object of the exercise. 

 

Nobody twigged to the fact that at top of climb everything was set up by the pilot for cruising, so at that time all the needles were pointing at what was wanted. It wasn't until 30 minutes later that the pilot noticed an anomaly - behind ETA - which would have started a search for a reason. That's when the reading of the ASI would have been noticed and, to quote Professor Julius Sumner Miller, ask "Why is it so?"

 

I'm amazed that no one has commented about the degree of RPM loss from the set RPM would be caused by a magneto failing. When I first thought of this, I figured that the reduction in RPM would have been a bit over 50, but not over 100. That would have been the same, say as going from a desired 75% power to maybe 70%, with a consequent loss of thrust leading to a reduced airspeed and therefore ground speed and time.

 

 

No mention that I can read about an RPM drop. Just set at 75% power with to me is an about setting say 5,000 rpm in my flights.

[M61A1]

1 hour ago, Yenn said:

My flights are spent with one hand on the throttle all the time. The cockpit is too small for it to be anywhere else.

On Saturday I was stooging along and all of a sudden saw that my Tiny tach was indicating over 5000rpm.

That is the only tach I use and it was new only a few hours ago. The Jab engine will not run to 5000rpm.

I know what happened, do you? I will fix it before next flight.

Either the tach was switched over to a different setting or you are getting extra signals from other cables with AC or other plug leads.

[old man emu]

1 hour ago, Blueadventures said:

No mention that I can read about an RPM drop.

No there wasn't

 

BECAUSE THE FIRST THING THE PILOT NOTED WAS THAT HE WAS LATE ON HIS ETA. 

 

HAVING NOTED THAT, WHAT WOULD A PILOT DO?

[M61A1]

10 minutes ago, old man emu said:

No there wasn't

 

BECAUSE THE FIRST THING THE PILOT NOTED WAS THAT HE WAS LATE ON HIS ETA. 

 

HAVING NOTED THAT, WHAT WOULD A PILOT DO?

Check the wind.

Power loss would have been noticed the moment it occurred.

[APenNameAndThatA]

So, the answer should have been. "Check to see if you are no longer at 75% power, your revs dropped or you are flying slower than normal".

 

No knowledge of systems was required to do the first step and check if you are flying slower than normal.

 

S T U P I D

 

 

[old man emu]

9 minutes ago, M61A1 said:

Check the wind.

OK. Did that. Aircraft is on track. Forecast winds are "light" which means 1 to 2.5 kts. But variable, could mean periods of calm.

 

5 minutes ago, APenNameAndThatA said:

So, the answer should have been. "Check to see if you are no longer at 75% power, your revs dropped or you are flying slower than normal".

After the pilot sees that the ASI is less than what it was when set up for cruise, looking at the tacho would be the next step. 

Then the question is, "Why are the revs down?" That leads into examination of the fuel/air mixture.

[Jase T]

10 hours ago, IBob said:

Okay, here's an easy one:

An aerial wildlife survey, undertaken in nil wind conditions, and which located a bear and several colonies of birds, where the pilot flew due east for 30 minutes, north for an hour, then south for an hour, returning to base.

What colour was the bear?

I was presented this question on pilots course  on a navigation exam as a "Bonus point" question..... I will leave it to those who haven't seen it before !!!

[Thruster88]

36 minutes ago, M61A1 said:

Check the wind.

Power loss would have been noticed the moment it occurred.

Agree with a fixed pitch prop. If the aircraft had a constant speed and the power was set at 23inch manifold pressure and 2300rpm and one mag failed what would the two gauges show and why. The engine should still run smoothly but there would be a power loss.

[Bruce Tuncks]

I reckon the bear would have been white Jase, on account of how only at the north pole could you do that nav stuff.

I had not seen that one before, but there was another one about the house where every window faced south...

 

[spacesailor]

 No east or west ?.

spacesailor

[kasper]

4 hours ago, Yenn said:

My flights are spent with one hand on the throttle all the time. The cockpit is too small for it to be anywhere else.

On Saturday I was stooging along and all of a sudden saw that my Tiny tach was indicating over 5000rpm.

That is the only tach I use and it was new only a few hours ago. The Jab engine will not run to 5000rpm.

I know what happened, do you? I will fix it before next flight.

Well either your picking up added pulses - tiny tachs run off the tripper wire coiled around the spark lead to a plug - or you have the wrong type fitted - they used to come in two stroke or four stroke and of course one reads 1 pulse = 1 rev while the other reads 1 pulse = 2 rev.  
 

but a jab engine is four stroke so I’m guessing the pulse wire is on the wrong lead or - and I don’t know this - the jab fires every rev and throws away a spark on the exhaust stroke and therefor need to be set to two stroke mode even though it’s a four stroke.  
 

😛

[Jerry_Atrick]

OME - sorry, but i am on the bandwagon with this one. I had a large number of quotes lined up, but the system lost them, and I am not trawling through them again. So I am going off memory. Firstly, the way in which the question was phrased was that it was a day of exceptionally stable conditions with relatively low humnidity and a decent gap between OAT and dew point - that one had set eveything for cruise and everything (including the ASI) was where it should be. The emphasis on all of this was that most of us interpreted these as being the same at the time of noticing the deviation from flight progress.  So, yes, you could normally say that after 30 minutes noticing the difference in expected and actual GS, the IAS would be a thing to check, but if this is the case, I think the question is disingeniously worded to trick us into assuming it was constant - I can't believe most of us would have come to the same conclusion if it were any other way.

 

For me, the other thing that led me to that conclusion that the power or throttle setting at least was constant (yes, there could be a magneto or some other fuel/air/spark system issue) was that the friction nut is set firm. I have never flown with a firm friction nut (no puns, please) and even in some fairly rough turbulence, have never had a throttle move on its own accord. So to me, highlighting it was firm was highlighting power at least, and assuming a fixed pitch, revs was constant (given we were already thinking ASI is constant). Also, even if it were firm and somehow in those conditions unwound, unless the throttle is spring loaded, there is a tiny chance (and in my experience, particularly given the conditions, no chance) it would change the power setting. Of course, a magneto can fail in flight and I have had that happen, with a detectable drop in RPM (in a Warrior).

 

So, yes, I feel the question inferred that the power and ASI was reading as expected after 30 minutes..

 

And in answer to your question about not doing checks for 30 minutes on those superb flights - er - no - never waited that long. And there are two reasons.. FREDA/CLEAR checks are not really nav related but systems related.. Secondly, I don't want to fly with a fuel imbalance, and thirdly, I want early warning of systems packing up. If I have have waited even 10 minutes to do those even on the most familiar routes I take, I would be incredibly surprised. And I now have a GPS which means I am often checking I am at least on track and it will tell me if my speed is off. Although, I take the point, that was not in the question.

 

Finally, in my tongue-in-cheek and other's more prudent answers, there was at least a strong inference, if not an explicit statement of assuming the VSI was reading as expected... this was not confirmed or rebuked... so for those answers (in so far as they were correct given those assumptions), the answers are just as valid as the assumption you had made. And asserting ignorance or falling short is not fair because that assumption was made. We are basically saying that we checked the IAS (in my answer I said I tapped the ASI), it was as expected so we moved immediatley onto other root causes.

 

In other words, the question was worded in such a way that it was inferred we all checked the ASI (and power/RPM setting) and as it was reading as expected, we started down a path that tried to find faults in pressure systems or the gauges themselves...

 

 

Edited October 16, 2020 by Jerry_Atrick

[IBob]

Wait....no.....here's the problem: icing!!!

[rgmwa]

26 minutes ago, Jerry_Atrick said:

In other words, the question was worded in such a way that it was inferred we all checked the ASI (and power/RPM setting) and as it was reading as expected, we started down a path that tried to find faults in pressure systems or the gauges themselves...

 

 

I agree. That’s how I understood it. What’s the next question? 

[M61A1]

3 hours ago, Thruster88 said:

Agree with a fixed pitch prop. If the aircraft had a constant speed and the power was set at 23inch manifold pressure and 2300rpm and one mag failed what would the two gauges show and why. The engine should still run smoothly but there would be a power loss.

RPM should still be 2300 ( constant speed),  manifold pressure should slightly lower as the as the engine would have unloaded slightly when the prop fined up to compensate unless the pilot increased power to compensate for reduced airspeed, in which case the manifold pressure would be higher.

That would be my best guess. I’m not educated on constant speed props, ask me about helicopters and I may be more helpful. 

[old man emu]

On 14/10/2020 at 2:00 PM, old man emu said:

You take off and set for cruise, checking that you have "Carby - Cold; Friction Nut - firm; fuel On and sufficient quantity; oil pressure and temp "in the green"; RPM set to 75% cruise power. The aircraft is trimmed nicely. The needle of the VSI isn't moving away from Zero. The arrow of the ASI points directly at your desired value.  God's in His heaven and all's well with the world.

 

This paragraph has got to be what was misunderstood. I described an initial situation where the aircraft had been set up in cruise configuration and the things that indicated that the set up was correct were checked and found correct - just after take off.

 

In some of my replies I mentioned that the pilot was flying TIBMIN. My mistake was in using an obscure acronym, (Thumb in bum, mind in neutral) implying that the pilot was carefree and enjoying the flight. So it is possible that the pilot was not being scrupulous in monitoring the instruments. It does happen.

 

So after a not so long period, the pilot sees where the plane is and finds that it is not where he expected it to be. After eliminating external factors affecting airspeed, the question was meant to turn attention to aircraft systems, and I thought that losing one magneto would be a pretty obscure cause. Homing in on that required a knowledge of aircraft systems. Sure, a lot of people went straight to the ASI, but failed to eliminate it by a logical process. But they stopped there. 

 

I even said  in response to an very early reply that attributing the cause to an ASI fault was not the answer. Thruster suggested loss of power and I said he was on the right track. Nobody took that up.

 

I know I have learned a lot from this about how people read and comprehend stuff. I ran what I had written through a style analyser and it concluded that the content would be comprehensible to a Year 6 student. 

 

1 hour ago, rgmwa said:

What’s the next question?

How much wood

Would a wood chuck chuck

If a wood chuck could chuck wood?

[rgmwa]

6 minutes ago, old man emu said:

How much wood

Would a wood chuck chuck

If a wood chuck could chuck wood?

Would that chuck be at take-off or in the cruise?

[M61A1]

51 minutes ago, old man emu said:

I know I have learned a lot from this about how people read and comprehend stuff. I ran what I had written through a style analyser and it concluded that the content would be comprehensible to a Year 6 student. 

The content was perfectly comprehensible. You just didn't write what you actually meant.

[Blueadventures]

14 hours ago, Jase T said:

I was presented this question on pilots course  on a navigation exam as a "Bonus point" question..... I will leave it to those who haven't seen it before !!!

If you made turns in the flight the bear could be black, black and white or white.  Black bear, Panda or Polar.😀

[old man emu]

18 hours ago, Yenn said:

I know what happened, do you? I will fix it before next flight.

I've tossed and turned over this problem all night. I've created a systematic diagnostic list and carefully used it to diagnose the problem.

 

The light bulb in the centre lavatory in Economy Class has blown.

[APenNameAndThatA]

The real value in this question was working out where it is wrong. The question states “the aircraft was trimmed nicely”. Aircraft are trimmed for speed, not altitude. Therefore, if the engine lost power, the aircraft would lose height, not speed. For a trimmed aircraft to lose speed but not height, it must have lost power AND have a trim problem. So, it was a systems problem after all! OME wins! 
 

Well, he would have, if he had told tge readers to ignore wind. The forecast and lack of turbulence are, of course, nonsensical nonsense. 

[APenNameAndThatA]

12 hours ago, old man emu said:

This paragraph has got to be what was misunderstood. I described an initial situation where the aircraft had been set up in cruise configuration and the things that indicated that the set up was correct were checked and found correct - just after take off.

 

In some of my replies I mentioned that the pilot was flying TIBMIN. My mistake was in using an obscure acronym, (Thumb in bum, mind in neutral) implying that the pilot was carefree and enjoying the flight. So it is possible that the pilot was not being scrupulous in monitoring the instruments. It does happen.

 

So after a not so long period, the pilot sees where the plane is and finds that it is not where he expected it to be. After eliminating external factors affecting airspeed, the question was meant to turn attention to aircraft systems, and I thought that losing one magneto would be a pretty obscure cause. Homing in on that required a knowledge of aircraft systems. Sure, a lot of people went straight to the ASI, but failed to eliminate it by a logical process. But they stopped there. 

 

I even said  in response to an very early reply that attributing the cause to an ASI fault was not the answer. Thruster suggested loss of power and I said he was on the right track. Nobody took that up.

 

I know I have learned a lot from this about how people read and comprehend stuff. I ran what I had written through a style analyser and it concluded that the content would be comprehensible to a Year 6 student. 

 

How much wood

Would a wood chuck chuck

If a wood chuck could chuck wood?

A trimmed aircraft would have list heigh, not speed. 🙄

[old man emu]

1 hour ago, APenNameAndThatA said:

A trimmed aircraft would have list heigh, not speed.

Theoretically, quite so, but it depends on where the centre of mass of the fuel load is in relation to the CofG of the aircraft, and also the weight loss from fuel burn in 30 minutes at 75% power. 

 

If one accepts that altitude would have changed, would that negate a search for the reason for the altitude change? Would not discovering a dud magneto be the result of that search?

[Garfly]

On 15/10/2020 at 9:30 PM, old man emu said:

 

 

The flight has been smooth and you are on track, but late. That could indicate a head wind, but wind doesn't blow in a steady stream. Any wind acting on the aircraft would have caused some degree of buffeting. You dismiss the head wind theory and look elsewhere.

 

 

I think I'd accept that I had a failed magneto, in accordance with Occam's Razor.

 

   Say what!!???    Where's my razor!!