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.

24 minutes ago, onetrack said:

So, essentially, what you're saying is - if your kitbuilt aircraft doesn't come with a POH, you should write one up, and include the important emergency operational checklist?

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? 

21 minutes ago, Yenn said:

Try another one OME, this has certainly got us all thinking.

 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.

37 minutes ago, IBob said:

 

I assumed from your scenario that was also the case 30minutes later, since I can't imagine any pilot would set and forget the throttle. Would they?

Did you question your assumption? The thing to consider is that after a period, the pilot first notices that something is out of place. It's a minor thing - running behind ETA. Shouldn't the pilot ask, "Why?" and then diagnostic process starts from there?

Let's look at the circumstances of the flight. Lovely day for flying; little or no effort required in pushing the aircraft around to counter the effects of wind. A small drop in RPM would hardly be noticeable from engine noise. Honestly, do pilots spend the whole of a recreational flight intensely scanning the instruments? Isn't the rule, keep your eyes out of the aircraft? Unless the pilot is aware, or has been warned, of the possibility of the throttle creeping closed, why would the pilot touch it after setting and securing it?

46 minutes ago, facthunter said:

Perhaps you would expand on EFFECT of the risk element and how you justify not continuing

That's a really good topic for another thread, but discussing it at the moment here would distract from the original reason for the exercise. 

I do agree that aircraft can be operated with permissible unserviceabilities, but in this case which is a superior result - continue to destination away from home and possibly being stuck there with a U/S aircraft, or turn back to base and get to sleep in your own bed and deal with the problem at your leisure? Sort of a reverse case of "get-there-itis"

What I have tried to make people think about in this exercise is formulating a systematic process to diagnosing a fault in an aircraft system. That process depends on knowledge of aircraft systems. I'm sorry to say that everyone has not met the required standard.

12 hours ago, M61A1 said:

You stated that the ASI was reading exactly where it should

I said that the ASI was exactly where it should be when "You take off and set for cruise". I didn't say anything about the ASI reading 30 minutes later. All I said was that 30 minutes into the flight you notice that you were running late. 

10 hours ago, Ryanm said:

you’re saying the ASI was indicating a slower than expected speed. Which would start to suggest a performance/engine issue. 

Why didn't you explore that idea further. You were on the right track.

People mentioned a blocked pitot tube, which can happen for a variety of reasons. If the blockage occurs on the ground, you will notice that your air speed indicator continues to read zero even as you begin to accelerate for takeoff.

An in-flight blockage likely won’t be noticed as quickly, however since the air speed indicator measures the difference between static and dynamic pressure, a blocked pitot will skew your dynamic pressure reading. When you ascend or descend, the static pressure will change while the dynamic pressure will remain artificially constant. Therefore, regardless of true airspeed, indicated airspeed will decrease as you descend and increase as you ascend.

In this exercise, the aircraft remained flying straight and level at the desired cruise altitude, so the the static pressure would not change. The ASI is reading lower than expected, so you could discount a blocked pitot tube.

The effect of loss of efficiency due to a failed magneto might only be small, but over time that can amount to a longer time to cover a set distance. As an example, taken from the POH of a C-152,  75% power at 4000' should yield 103 kts, while 65% power will yield 97 kts (still wind conditions). It's a case of pennies make pounds, or for you young bloods, cents make dollars.

The exercise was aimed at testing both knowledge of aircraft systems, and the ability to develop a systematic procedure to diagnose a problem. Nobody produced any sort of procedure, just jumped on one thing.

I will take a it on one thing - airmanship. Thirty minutes into a flight and a fault is discovered, yet I am prepared to press on. A wise pilot would have turn back to Base, if only to ensure that s/he could get to s/his car to drive home.

1 hour ago, Jim McDowall said:

A report commissioned by Government and authored by a properly credentialed firm would have more credibility.

At least a report prepared by an independent body.

OK. Not one of you has provided a systematic scheme for working out what is going on here, and, despite my saying that knowledge of aircraft systems would solve the problem, the best that people have come up with is a faulty ASI.

Here's the original data, so let's go through it:

It's Sunday morning and you and your "significant other" decide to take a flight to get a $100 hamburger at a beach side airport. You check the weather and find that your intended flight path is dominated by a strong high pressure cell of up to 1024 hPa and winds are light and variable below 5000. Temperature is in the low 20's; humidity in the 40's and dew point is below 10C.

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.

1.  The flight will be through a very strong High pressure area within which winds will be light and variable. Light and variable means there's no meaningful wind speed or direction.  It will also mean that the aircraft will be very stable - nothing to knock it off straight and level flight.

2.  The air temperature is nicely above freezing level and humidity is low, so you won't need to constantly watch for carby icing.

3.  At Top of Climb you have established the aircraft on course and in straight and level flight with engine power set.

4.  You fly along for 30 minutes, watching the scenery and notice nothing untoward. However, after 30 minutes of smooth flight you determine that, while you are on your intended track, you are behind your ETA.

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.

You scan the instruments and see that the ASI is reading less than what you expected. What can cause this? It could be a problem in the pitot system, or it could be reduced thrust.

The simplest reason is that the engine is not producing the thrust normally expected at a certain throttle setting. Then take a look at the tachometer. If it is showing a reading lower than what was set at top of climb, there could be a problem with the engine.

Three things could be the simple cause of that. Check are the throttle friction nut. If the nut has wound itself out, the throttle rod could have walked backwards, reducing power. Check that the nut is tight. Likewise the mixture control could have wound itself out. Check that. the carburettor heat could have started to bring itself on. Check that.

To run an engine, you need two things - an air/fuel mixture and a spark. You've checked the things that affect the air/fuel mixture (the assumption is that since the flight has been smooth and unremarkable, that the fuel supply is OK). That only leaves the spark.

Remember when you did the pre-takeoff engine checks? You ran the engine to 1500 RPM, or whatever fast idle was for the engine, then you checked the magnetos, carefully noting the drop in revs as you switched from Both to Left of Right. At fast idle we expect a rev drop whose size is dependent on the engine.

A 75% cruise power setting results in engine RPM well above those of fast idle.  If shutting off a magneto at, say 1500 RPM gives a 50 RPM drop, what sort of RPM drop would you get at the higher RPM of 75% cruise? That RPM drop would result in less thrust, resulting in a lower air speed and hence a lower ground speed. That's could be why you are behind ETA. One of the magnetos has failed.

Remember I said that this diagnosis depended on your knowledge of aircraft systems.

I think I'd accept that I had a failed magneto, in accordance with Occam's Razor. The redundancy in the ignition system gives me faith that I can complete my flight, but maintain greater vigilance, and I'll look at the magnetos after I land at the beach side airport while my significant other is having a hamburger.

6 minutes ago, M61A1 said:

If you consider it enough of a problem

You had better strop Occam's razor, 'cause it's as blunt as.

As you are told in all examinations - read the question carefully and think about the information it gives you.

1 hour ago, facthunter said:

Do your usual monitoring

Why? What will that tell you?

1 hour ago, M61A1 said:

You could get a job writing CASA exam questions OME. 

This one's sure exposed a lack of knowledge.

27 minutes ago, rgmwa said:

the simplest explanation is “something’s gone wrong”.

Getting to the answer! 

What lead you to the plan to add more revs?

I was betting that Facthunter would solve this easily.

Here's a clue: 

The answer can be found by the use of Occam's razor.

Occam's razor is the principle that, of two explanations that account for all the facts, the simpler one is more likely to be correct.

I'm starting to wonder if allowing pilots to maintain their aircraft is a good idea. I'm not seeing any listing of the actions being taken to diagnose the problem. So far only two people have hinted at aircraft systems and one of those persons is wrong.

As for the half hour to notice that achieved ground speed was not as planned, I said that the pilot was flying a familiar route TIBMIN and enjoying the view.

2 hours ago, Thruster88 said:

I feel you are suggesting there has been a slight loss of power, does the aircraft have a Constant Speed propeller to complicate the diagnosis 🤔😂🙄

No. Fixed pitch prop.

I think that Thruster might win the prize. Remember, you note that track made good is right on planned track.

3 hours ago, RFguy said:

so how come my original answer
"headwind ? Pitot / static system ?  incorrect IAS-TAS conversion for temp,hum,press ? " is incorrect ???

The scenario does not provide data for that. Read the scenario again.

Nobody has listed the actions they would take to diagnose the situation. That's where the answer lies.

You can't answer the question until you have checked the aircraft's SYSTEMS.

1 hour ago, M61A1 said:

I want to know why it took half an hour to realise there's an issue.

'Cause it's a lovely day and you've flown this route umpteen times. You have been sitting there enjoying the view TIBMIN.

The weather system is a stationery High Pressure one that hasn't moved for a couple of days, and is not forecast to move for a few more days.

1 hour ago, M61A1 said:

do you want us to tell you why the wind is variable?

No. Note the tag to the thread - "Systems Knowledge"

Nobody has yet said what actions they would take to diagnose the cause.

Very interesting RFguy, but no

Read the scenario again.

Can you diagnose this situation and explain it's cause?

It's Sunday morning and you and your "significant other" decide to take a flight to get a $100 hamburger at a beach side airport. You check the weather and find that your intended flight path is dominated by a strong high pressure cell of up to 1024 hPa and winds are light and variable below 5000. Temperature is in the low 20's; humidity in the 40's and dew point is below 10C.

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.

After about half an hour you cross-check your flight plan, map and GPS and find that your ground speed is a few knots less than expected, and you are behind ETA, but dead on track.

What actions do you take to diagnose why you are slow and late, and what could be the cause?

2 hours ago, Kenlsa said:

Pen reared fish fed on human excrement.

I was buying fish fingers, too. The Woolies ones were beside the Birds Eye ones, and labelled "wild caught".  The were also labelled "Made in China" 

Aye, Aye, Cap'n Birdseye! 

The wife put wrapped cheese slices on the shopping list she sent me out with today. I grew up eating Kraft Cheddar Cheese which came wrapped in silver paper in a cardboard box, so I reached for the Kraft Cheese slices. I decided to have a look for the origin of the product. "Made from at least 20% Australian content."  Where does the other 80% come from? On the other hand, Woolworth's own brand claimed 90% Australian content. I did notice that Coon Cheese was from Warnambool, but let;s not reignite to "coon" thing.

8 hours ago, onetrack said:

We are surrounded by the greatest Oceans in the world, with the best fish stocks, and the best-tasting fish, and we should not be importing rubbishy Asian fish

That's because we export all our high quality, healthy fish to Asia for the rich Chinese, Japanese and South Koreans.

Perhaps we should all go to supermarkets with our Smartphones and take photographs of the labels on foodstuffs that show that Coles and Woolies are selling us non-Australian products.

Another thing I'd like to see are the figures on how much of the extra money Coles and Woolies added to the "Drought Relief" milk actually ended up with the blokes pulling the teats. And that money would have only gone to farmers who sold their milk to the big milk companies like Dairy Farmers, Peters and Devondale. Those who sold to independent milk companies would not have got a razoo. 

I bought a roll of packing tape this week. It proclaimed that the company was all Australian owned. But the tape was made in China. So it's not the Australian-owned companies you should deal with, but you should only buy things that are made from a very high percentage of Australian products.

55 minutes ago, onetrack said:

killing everyone on board

And provided more fodder to the ignorant meeja about the safety of light aircraft. It's amazing that killing four people while hooning in a motor vehicle doesn't elicit the same hysteria in the meeja that a bumpy forced landing in a small two-seater aircraft does.

2 hours ago, cscotthendry said:

I can't be bothered performing CPR on suicide attempts.

An interesting dilemma. Which is the greater duty - to preserve life or to respect another's control over their life?

If one chooses to preserve life, then the logical corollary is to abolish those threats to life that one is able to - such as the use of tobacco; over-use of alcohol and the abuse of natural and man-made drugs.

1 hour ago, RFguy said:

the different types of CO detectors, the low end ones ($50) are accurate but they're also sensitive to other gases. 

Is that such a bad thing? Any chemical detector should be sensitive to the its designed chemical. If it is, great. But if it also detects other chemicals that we don't really want, then that's a plus. Imagine if your CO detector also happened to react to CO2. That is a dangerous gas in a confined space, and is a gas likely to be encountered in the cockpit.

Also, we can only use up to 21% of the volume of air we breathe in. That's all the oxygen that is usually in it. If we go putting other gases in, even vapours like water and fuel vapours, we are reducing the amount of oxygen we can take in with every breath. I suppose that our body's protection system has developed so that if we can smell something, there's too much of it in the air. Try going near a teenage boy who has a can of Lynx.