Tachometer reading incorrect

[Molesworth 1]

The a/c I hired yesterday had a tachometer which was over-reading by between 300 - 500 rpm, making it just about useless - my passenger wondered why I kept changing the power settings on final.

Is there any way of checking for this on the ground besides putting on full power in the run-up checks?

[foxmoth]

I think you will find most engineering setups will have a strobe they can use to check RPM.:ok:

[Mariner9]

Preplanned RPM settings can only ever be approximate on final, the setting required depends on a number of factors including position in the glideslope, a/c loading, headwind etc etc so I don't see myself why an incorrect tach could cause any significant problem on approach.

However, if it did indeed over-read to that extent, surely this would have been apparent at both full power and idle power checks?

Could it just be that the prop on that aircraft has a finer pitch to others you are used to flying hence requires a higher rpm for a given glideslope?

[BackPacker]

Was it placarded as overreading, or did you find out yourself. And if so, how?

And how much did you pay when the flight was over? If the tacho RPM overreads significantly, then so will the tacho counter. If the rental price is based on tacho hours, then you'd be charged 1.2 hours or so for each hour flown.

[Molesworth 1]

foxmoth

I don't think checking the tachometer with a stobe would be practical every time I fly.

Mariner9

The approach was still flyable and of course the power setting depends on a number of factors, but without the tachometer one doesn't know what power setting one has selected and that doesn't make life any easier. It's quite possible to do an approach without an ASI too, but I'm not going to try!

Yes - I probably should have realised there was a problem when doing my power checks, but the mag checks were fine. It's even possible the problem developed during take off. The a/c had been flown previously that day by an instructor and he obviously hadn't noticed it.

It's possible too that the error was not linear over the whole range - being greater at the high end.

The propellor was of the fixed pitch type.

BackPacker

I found it out myself - some time after leveling off after take off. This would have meant I had done my power checks at 1200 rpm rather than 1700 rpm. Also if the engine had not been producing full power on take off I would have been misled into thinking it was. I probably would have realised this by sound alone, but one can't always be sure.

The flight was charged by time and not tacho hour so I wasn't over-charged.

[Pilot DAR]

If the tach is really out that much, it should be replaced. In Canada, a 5% error is the most which will be tolerated to be placarded. Such errors can allow engine or propellr speed limits to be exceeded in some cases. Not good. They can also really make some performance charts inaccurate.

If in doubt, have the tach check optically - it's easy. Generall older tachs cannot practically be adjusted, as their cases are crimped shut. Buying a new tach is generally the only soultion.

Pilot DAR

[Molesworth 1]

I suppose what I am asking is how does one spot this accurately during a normal "A" and power check?

[BackPacker]

I suppose what I am asking is how does one spot this accurately during a normal "A" and power check?

After a certain time flying a certain aircraft, you know the sound an engine makes at a certain RPM. That will give you a rough indication.

If it's a recent failure of the tacho, then the idle RPMs will be very abnormal, while the engine idle settings have not changed. Likewise, when starting the take-off roll, there are minimum and maximum RPMs that you should see when applying full power.

Another way is by setting cruise RPM and not getting the associated cruise performance (IAS). But then again that might be caused by a faulty pitot/static system or faulty ASI too, so double-check with DME/GPS and correct for wind.

But indeed, those are general indications and not very accurate.

[Molesworth 1]

Backpacker

Thanks, that's useful.

I fly a different aircraft (although the same type) very time. Idle indicated in excess of 1000 rpm which I should have noticed as far from normal (although the setting does vary considerably).

It was in the cruise that I first noticed it and it was possible then to gauge fairly accurately the extent of the over reading.

[englishal]

What was the tach reading on take off? If I was taking off in a SEP with a Lycoming type engine and the tach read over 3000 I'd probably return and land.

[Mariner9]

Surely if it overread it would have redlined on the takeoff roll. What rpm did you have on the climb out?

[worrab]

Crikey!

Ground check: at take-off the tachometer off the end of the green arc when full power commanded?

[Molesworth 1]

Surely if it overread it would have redlined on the takeoff roll. What rpm did you have on the climb out?


From what I recall it was 2700 - 2800 rpm - yet I had to cruise at 2500 to get my 90 knots.

[Big Pistons Forever]

I insist all my students know what the static RPM limits (fixed pitch prop) are for the aircraft they fly. It is considerably lower than the redline. For example the C 150 has a 2700 RPM redline but the POH lists the static RPM as 2460 to 2560 RPM. I teach all my student that as soon as the throttle has reached the full in/forward position (after being slowly and smoothly advanced at the start of the takeoff role) they check the RPM (looking for static RPM value) and engine gauges (looking for all in the green) and verbalize the call "good engine". In molesworth 1 case I would expect my students to have rejected the takeoff at the engine check point because the RPM would have been at or over the redline RPM and therefore not at the expected static RPM value.

[Molesworth 1]

Well its one more issue to add to the list of things I now know can go wrong which I didn't learn in my PPL course. My present flying club has been very helpful in this respect.:E

The older Cessna's don't have a green arc - they might well have a red line although I've never been consciously aware of it.

Is there any other reason the tacho could be over the red line? The propeller falling off?

[Gertrude the Wombat]

It's quite possible to do an approach without an ASI too, but I'm not going to try!
You should.

People have killed themselves by screwing up an approach with a dead ASI, which is quite unnecessary.

Fly a circuit with an instructor and the ASI covered up.

[NutLoose]

Amother reason is that a prop can "untwist" if its not the tacho this happens over a time so its not working so hard and the revs rise slightly....... Overhauling the prop you can have it set to be a climb prop or a cruise prop... If they can, ask them to swop tachos with another one if they have 2 or more aircraft, see it it makes any difference.

Have had one over revving in the past and took it up with both Cessna, Lycoming and the CAA.

Cessna stated read the book that says go by Lycomings figures. ( which I had)

Lycomings figure for the static rated RPM for the Engine was higher than the Cessna figure by quite a large amount and even swopping props with an overhauled one or renewing the RPM gauge I was able to reduce the figure...

The Overspeed limits took it well over what it was ever achieving so It was left alone and quite happily revved through the redline on take off but was below Lycomings acceptable figure. So it lived like that for a thousand of hours or so until the prop was eventually replaced again at overhaul, and now it is back where it should be.......... oddly it's prop went on another aircraft and is fine on that one, go figure.

If the rpm gauge is fluctuating this can often be a worn tacho drive cable as the inner whips around inside the outer allowing it to happen.....

Lycomings figures and determination of overspeed / overboost are here on their website for you all.

http://www.lycoming.textron.com/support/publications/service-bulletins/pdfs/SB369J.pdf

So as an example a Cessna 152 that is on the Type cert as

Engine limits S/N A1500433, A1520735, 681 through A1521014
For all operations, 2550 r.p.m. (110 hp.)
S/N A1521015 and on
For all operations 2550 r.p.m. (108 hp.)

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/a01fa66c9a3bc9498625745100674f44/$FILE/3A19.pdf

on Lycomings figures the O-235-L2c as an example is actually rated at 2800 RPM

[Molesworth 1]

Fly a circuit with an instructor and the ASI covered up.


Have done - except for the last bit of final.

[Gertrude the Wombat]

Have done - except for the last bit of final.
So do that as well.

Yes you will be coming in a bit faster than usual, yes you will need a decent length runway, no you won't know exactly how fast you're going.

So you just fly along the runway a couple of feet up until it stops flying and you land. No problem, just don't try it on 450m of grass, if it happens to you for real divert to somewhere with a couple of kilometres of tarmac, that's all really.

[SNS3Guppy]

Cessna stated read the book that says go by Lycomings figures. ( which I had)

Lycomings figure for the static rated RPM for the Engine was higher than the Cessna figure by quite a large amount and even swopping props with an overhauled one or renewing the RPM gauge I was able to reduce the figure...


The only figures you can use are the type certificate data figures. These are what must be determined when performing an inspection. Lycoming may have engine limits, but this says nothing about propeller limits, and propeller limits say nothing about engine-propeller limitations.

These are spelled out in the type certificate data sheets for the airplane. That Lycoming states the engine may be run to a particular RPM is meaningless. The only figure that has meaning is the one established for the engine-propeller combination, specifically the one found in the TCDS.

Amother reason is that a prop can "untwist" if its not the tacho this happens over a time so its not working so hard and the revs rise slightly....... Overhauling the prop you can have it set to be a climb prop or a cruise prop... If they can, ask them to swop tachos with another one if they have 2 or more aircraft, see it it makes any difference.


"Untwisting" fixed pitch propellers?

There's little point swapping tachometers if you can't verify the calibration of the replacement tachometer.

The answer here is to verify the actual propeller RPM, first. If you don't know the actual propeller RPM, then you don't know anything, and no matter what you do from then on, it's purely guesswork with no baseline for comparison.

[Pilot DAR]

Amother reason is that a prop can "untwist" ..... when you run it through soft ground perhaps.

If it is fixed pitch, and airworthy, you can stake your life on the blades being where they were last manufactured or overhauled to be. Because you are staking you life on it.

In today's technological world, forget the inaccuracy of charts, and just use a portable optical tach to check the installed one. The optical tach can be calibration checked when pointed at a flourescent light.

[Pilot DAR]

Here is the wording of the Canadian requirement for tachometer airworthiness:

8. Tachometers
The accuracy of mechanical drag cup type tachometers, for fixed wing propeller driven aircraft, shall be checked on site annually, and be accurate to within the tolerances established by the aircraft manufacturer or, where no tolerance has been specified by the aircraft manufacturer, to within +\- 4% of engine RPM at mid-point of the cruise range.
(amended 2000/12/01;

[NutLoose]

[quote]
Quote:
Cessna stated read the book that says go by Lycomings figures. ( which I had)

Lycomings figure for the static rated RPM for the Engine was higher than the Cessna figure by quite a large amount and even swopping props with an overhauled one or renewing the RPM gauge I was able to reduce the figure...
The only figures you can use are the type certificate data figures. These are what must be determined when performing an inspection. Lycoming may have engine limits, but this says nothing about propeller limits, and propeller limits say nothing about engine-propeller limitations.

These are spelled out in the type certificate data sheets for the airplane. That Lycoming states the engine may be run to a particular RPM is meaningless. The only figure that has meaning is the one established for the engine-propeller combination, specifically the one found in the TCDS.


As in the example on the 152 for overspeeding the manual says refer to the figures provided by Lycoming that are higher, Not happy with that I faxed Cessna who came back to me and confirmed that if it was over the type Cert figures refer to what the manual is telling you for overspeeding ....... I have it in black and white. it tells you no action is required for the amount we had and to refer to Lycomings engine figures and overspeed data, I then contacted Lycoming who confirmed the figures and spoke at length with the Civil Aviation Authority with all the information at hand and they concurred.



Quote:
Amother reason is that a prop can "untwist" if its not the tacho this happens over a time so its not working so hard and the revs rise slightly....... Overhauling the prop you can have it set to be a climb prop or a cruise prop... If they can, ask them to swop tachos with another one if they have 2 or more aircraft, see it it makes any difference.
"Untwisting" fixed pitch propellers?


Fix pitch props do untwist, that is why there is a requirement when overhauling a fixed pitch prop to check the angles and retwist it. We in the UK now have to overhaul fixed pitch props at their designated overhaul periods and they are no longer on condition.

There's little point swapping tachometers if you can't verify the calibration of the replacement tachometer.



If you have a known aircraft on your fleet that is not over revving or known to be it is a simple job to swop tachos if you do not have the facility to calibrate it to check its reading.

[gasax]

A surprising topic.

If you think the tacho is over reading by 300 to 500 rpm then you should never have left the runway. Given the average spamcan's static rpm it would have been on the redline early in the takeoff run.

Even more importantly if it had been under reading, the engine could have been severely down on power. This is the last chance you have to check the aircraft is going to perform the way it is supposed to and clear the far hedge, fence, wall, hill.

Obviously if you are chasing rpm settings you do not have much experience - but do read the flight manuals and KNOW the expected static rpm from the aircraft at full throttle - if you do not get that do not fly. It can save more than just embarassment!

[Croqueteer]

:ok:My mechanical tach failed, so I tried a "Tiny Tach" digital tach bought on ebay for £25. It is spot on accurate , easy to fit and takes up minimum space.

[Molesworth 1]

Even more surprising was that I had been chatting to the instructor who had flown the a/c just before me and he never mentioned a word about it - nor did he report it in the tech log.

er.. except they have a post-it note system and nothing gets written in the tech log. I really need to have a chat to someone at the CAA about this sort of thing sometime:E

[gasax]

If that sort of practice is really happening then your first step might be the club - then the CAA.

But for your own sake learn how to assess whether the aircraft is flyable or not. Yes you might expect a club to go a long way towards helping you. But there are any number of mechanical and other issues which can all occur with little warning - from one flight to the other.

If you cannot make a 'go, no go' on your own initiative and knowledge then you should perhaps consider whether flying is a smart recreation?

I'm not trying to be especially smart, but for your own and your passengers health this is a skill you need. There is little more annoying than being stranded somewhere with a 'duff' aircraft - unless it is 'being up there, wishing you were down here'.

[Mike Cross]

The older Cessna's don't have a green arc - they might well have a red line although I've never been consciously aware of it.

Perhaps you should be aware of it. In any aircraft with a fixed-pitch prop it's very easy to exceed redline by failing to reduce power in a shallow descent. Just as pulling too much G can cause permanent damage that later kills someone, overspeeding can cause damage that later results in engine failure or the catastrophic loss of part or all of a prop blade. (In some, the V-tail Bonanza for example, you can get the opposite problem, a shallow dive with cruise power can make you exceed Vne and pull the tail off.)

You make an assumption that RPM = Power setting for a given aircraft type, which is not a good idea. For a given power output, all other conditions being equal, RPM will vary according to the prop fitted (and of course its condition).

The prop is every bit as much of an airfoil as the wings.

(edited for peer spolling)

[worrab]

my passenger wondered why I kept changing the power settings

I remember vividly my first lesson in landing: "One hand on the power, one hand on the stick and I want to see your eyes moving from the air speed to the runway. Use the stick to adjust your speed and your power to sort out the height". Now I know there's plenty of debate about the last bit, but unless it's completely calm with no ups and downs, I can't really see how you can always give yourself a half-decent chance of a good landing without changing/adjusting the power in the final descent.

[BackPacker]

I can't really see how you can always give yourself a half-decent chance of a good landing without changing/adjusting the power in the final descent.

Okay, I'll bite. It's true that the approach technique that's currently taught in powered flying is to approach *below* the zero-power glidepath, and use engine power to maintain your desired glide path. But that's by no means the only technique. You can also approach *above* the zero-power glidepath, reduce the throttle to idle and vary the drag (flaps, airbrakes, sideslips, forward slips, s-turns, you name it) to maintain the desired glide path. Gliders do this all the time and although this technique might not be desirable in a busy (power) circuit, it's a good technique to master.

[Molesworth 1]

If you cannot make a 'go, no go' on your own initiative and knowledge then you should perhaps consider whether flying is a smart recreation?


Not a very appropriate comment, me thinks!

Gasax, I'm a bit confused by your previous post as you seem to be saying I should have noticed the tach red lining and aborted take off yet in the next breath you seem to imply that if I was more experienced I wouldn't be relying on the tach.

I checked my PPL literature and there's no mention at all about tach failure or misreading. Presumably not all aircraft even have one. On the take off roll the emphasis is on checking the tach to see if full power is being generated. It doesn't take much experience with an aircraft type to sense intuitively whether the aircraft is producing full power - if you're airborne and not even a third the way down the runway can one not reasonably assume all is well? No instructor has ever mentioned a red line and I don't recall reading about it in the C152 hand book. I'm pretty sure there isn't one in this aircraft's tach or if there is it is so faded as not to be noticeable.

While I appreciate the advice given by others in this thread and it is certainly helpful I get a bit annoyed by ppruners who see it as a chance to have a go at anyone they feel is not as "experienced" as they.

[BackPacker]

No instructor has ever mentioned a red line and I don't recall reading about it in the C152 hand book.

Try the "limitations" section of the POH. Under "engine".

I did not find a full C152 POH online quickly, but stumbled onto this thing which is an (uncertified) summary: http://www.ginecoweb.com/Piloto%20Privado/Cessna152Manual.pdf. Page 3. 2550 RPM.

[asyncio]

You can get the full 152 POH here
Cessna FREE Manuals (http://www.micro-tools.net/pdf/Cessna/)
Which confirms the 2550 RPM limit.

[Molesworth 1]

If that sort of practice is really happening then your first step might be the club - then the CAA.


I need to check first with the CAA as to the correct procedure. For all I know the "post-it note" system might be perfectly legit.

[gasax]

For the avoidance of confusion - and nothing else!

As you open the throttle one of the first things that should be checked is whether the aircraft is making the 'full power' static rpm. With a fixed pitch prop and at the density altitudes we get in the UK that will be in the range of 2100 to 2400 rpm across virtually all spamcans. The specific rpm for your model/year etc should be known to you.

If you do not get that rpm then shut the throttle and find out why. Could simply be the carb heat left out - or the engine may be knackered. Over reading is rarer but if for instance an O-200 has more advanced timing the rpm goes up - but only some O-200s can withstand this without cracking!

In the approach configuration the rpm is whatever you need. If could be anything between the idle and near full throttle depending what else is happening - so as long as the engine is running, the tacho will tell you nothing about the state of the engine.

Have a look at a couple of recent accident reports where deterioration of engine performance has had a major influence - the recent Sandown Cherokee one springs to mind.

It is unfortunately a fact of life that the standard of and content of, much of what you are taught during a PPL does not give you the information you really need to operate outside a club environment.

If the club are also 'sailing close the the wind' think seriously about going somewhere else.

[Molesworth 1]

thanks gasax

Just had a word with an Airworthiness Surveyer from the CAA. Without my prompting his response was that the tach was "erring on the safe side" but would make setting the power setting on approach difficult.

Also I can insist on entering the "Defects" column of the tech log - which is what I will do from now on unless the fault is minor.

[IO540]

I'd get this fixed. Near the top end, the engine power output varies drastically with small changes of RPM and if the RPM is not set accurately, the fuel flow will be nowhere near the POH value. Combine this with somebody pushing the boundaries a bit on fuel planning....

[Pilot DAR]

Hey Molesworth,

You are entitled to grow and learn in aiviation, as others of us have - to whatever degree (it can be difficult to determine on PPRuNe, particularly from just a few posts).

That said, it is your obligation to grow and learn.

The PPL is a "license to learn". There is just no way that a person can learn much beyond just being safe, during such a short training time. You'll have upwards of a thousand hours, and still find yourself learning. I have many times that, and learn new things regularly - even here! Though happily, the learning curve seems to be flattening out now!

You will find that as flying becomes "second nature" the actual readings of instruments at any moment will be less important to you (though you still must know and operate within limitations, whether properly marked or not). "Second nature" opens the door to complacency, but that's beyond the scope of this post.

As for unless the fault is minor. that's a Pandora's box for new pilots. New pilots probably cannot correctly judge "minor" vs. "major" correctly. An informal chat with the maintainer of the aircraft you fly, will bring you up to speed on what people are looking for. By the way, the absence of a correctly located, visible red line on a tach would definately be "major" and snag worthy.

For your reference, here's a guidline for the "major minor" determination in Canada. It can be carried across to un modified aircraft condition fairly well too, just read "suspected defect" in place of "modification"

Canadian Aviation Regulations - Part V, Standard 571, Appendix A (http://www.tc.gc.ca/civilaviation/RegServ/Affairs/cars/Part5/Standards/a571sa.htm)

Pilot DAR

[TheGorrilla]

While flying around the local area my friend in the front seat of my Cub pointed at the taco/rpm guage, which had sprung from 2100 up to 3600.

She said "that doesn't seem right?!" (while pointing furiously at the thing - she's a pilot too!)... I said "no, it isn't. But that's a lovely view and down there and I reckon that pub would be a great place for lunch". After an hour or so we landed.... Happy days. :)

Few weeks later we changed the taco drive cable.

[Molesworth 1]

Gasax and Pilot Dar,

You are absolutely right. I am indeed learning quite a bit post-PPL - and none of it from an instructor either!

It's good - I can't understand pilots who give up flying - for me it becomes more interesting with every flight.

[Pilot DAR]

Good for you, being interested is probably the best way to be safe!

Pilot DAR

[Molesworth 1]

I did not find a full C152 POH online quickly, but stumbled onto this thing which is an (uncertified) summary: http://www.ginecoweb.com/Piloto%20Pr...a152Manual.pdf. Page 3. 2550 RPM.


I have finally got round to reading this.. and it's a real gold-mine - especially in regard to emergency procedures!

I also found a picture taken by my passenger while the a/c was cruising at aprox 90 knots.

http://i446.photobucket.com/albums/qq182/DavidHoul52/2009-07-04_0970.jpg

[BackPacker]

Well, the red line is definitely there, right where we predicted (at 2550 rpm) and you were definitely over it. Not good.

What makes it worse is that you apparently have a habit of setting your cruise power based on the ASI (you wanted to get 90 knots) instead of the RPM gauge. That's not as it's done by the book but it's actually a bit dangerous too: Suppose there is a block in your pitot/static system somewhere (insect in pitot tube - it happens!) then the ASI is underreading and you would be overspeeding the engine, even with a correct RPM gauge, to get the desired airspeed. The exact same thing would happen if your airframe is somehow "dirtier" than normal, either because of bugs and other dirt, or something else that increases the drag (wheel pants taken off for maintenance for instance).

Next time, at the top of the climb, first set the cruise attitude, let the aircraft accelerate (under full power) to an approximate cruise speed, then set cruise RPM. Trim, and then verify that your cruise RPM gives you the desired cruise performance (ASI).

[Molesworth 1]

Backpacker

I would expect to see about 2200 rpm in the cruise. That's when I first noticed the tach was out (should have noticed it earlier, but as I have said, I had no previous experience or instruction on this kind of fault - it was totally unexpected). Of course, as you say it could have been the ASI that was overreading, but given the sound of the engine, performance and so on I decided the tach was the faulty instrument.

Mistakenly assuming the tach as correct (which indeed is what we are taught) and suspecting the ASI could in this case have lead to a stall on final.

I made the right decision.

Any instructors out there - maybe make a note to mention the red-line issue to your students?

[BackPacker]

Mistakenly assuming the tach as correct (which indeed is what we are taught) and suspecting the ASI could in this case have lead to a stall on final.

I would certainly hope you were taught better than that!

Go fly a few circuits with an instructor with the ASI covered up. Or even better, go out and do some airwork (stalls particularly, but also steep turns) with the ASI covered up, then go and do some circuits.

Relying on the ASI as your sole indicator of an imminent stall is very dangerous, and is not making use of all other clues that precede a stall.

I made the right decision.

Continuing the flight with an instrument consistently indicating out of the limits? Not sure I agree with you on that statement. You didn't break anything, this time, but that doesn't mean the decision was right.

[Molesworth 1]

Backpacker

I meant - the decision to trust the ASI rather than the tachometer.

I don't agree with you about it being the wrong decision not to continue, either. I had to make a quick assessment of the situation. Adjusting the power to 2200 rpm in cruise meant I was unable to maintain height. So what does that tell me? Obviously if there was any other indication of the engine being outside limits it would have been a different story.

Without any other indication of engine malfunction and given that the flight was short in any case I didn't see that returning to the departure airfield immediately was necessary.

I can't believe that you really want me to fly by RPM readings on final approach? Especially considering that all the evidence pointed to the tachometer reading incorrectly. I know it's possible to fly without the ASI on final, but honestly - air speed is absolutely critical at this stage.

Being PIC means having the privilege and responsibility of making a decision and standing by it. Sometimes with hindsight and more information one discovers that a better course of action could have been taken. Not this time!

[BackPacker]

Adjusting the power to 2200 rpm in cruise meant I was unable to maintain height. So what does that tell me?

It tells you that the aircraft is not performing as it should. It doesn't tell you what causes that. As said, it can be an ASI malfunction, an RPM gauge malfunction, or an airframe that's somehow "dirtier" than normal, for instance because of a flap failure, failure to detach the tie-downs before taking off, a piece of cloth blown onto the tail, the previous pilot forgetting to remove the dead horse from the back, you name it. The aircraft we fly typically don't have dual-everything so there is no way to cross-check and *know* that a single instrument is failing.

Better find out what's wrong on the ground, not in the air.

And if you could not maintain altitude with 2200 rpm, why not limp home at 2550 (redline), which should give you about 80 knots? Why continue the flight over the redline limit at 2625?

Obviously if there was any other indication of the engine being outside limits it would have been a different story.

The next indication of an engine overspeed would most likely be a spectacular and catastrophic failure. A propellor blade detaching, a piston working its way out of the cowling due to a broken conrod, that sort of thing. But an engine overspeed doesn't lead to a gradual increase/decrease of oil pressure/temperature, which are the only other indicators that you'd have available.

So any single indication that's showing over the limit is reason to abort the flight, as far as I'm concerned.

I can't believe that you really want me to fly by RPM readings on final approach? Especially considering that all the evidence pointed to the tachometer reading incorrectly. I know it's possible to fly without the ASI on final, but honestly - air speed is absolutely critical at this stage.

What is the length of the runway you were flying from? Was that anywhere near the minimum required? Otherwise the airspeed on final, assuming a sufficient margin above the stall (no pre-stall buffet, no stall warner, no significant pull on the stick/yoke), is not nearly as critical as you think. That is, if you learned to land properly, bleeding off any excess speed in the flare.

Being PIC means having the privilege and responsibility of making a decision and standing by it. Sometimes with hindsight and more information one discovers that a better course of action could have been taken. Not this time!

So what you're saying is that next time you'll happily boost the engine over its redline RPM again?

[bjornhall]

of a flap failure, failure to detach the tie-downs before taking off, a piece of cloth blown onto the tail, the previous pilot forgetting to remove the dead horse from the back, you name it.

Getting silly now... :hmm:

Meanwhile, in the real world, the pilot had no problem correctly diagnosing the problem and taking the appropriate action... Bit strange if someone flying a familiar airplane could not tell 2200 RPM from 2600 RPM from the sound of the engine. Bit stranger if engine RPM was 2600 RPM with the throttle pulled way back simultaneously with the ASI underreading (2 simultaneous independent failures). So there are indeed ways to crosscheck the indications.

[Molesworth 1]

Thanks for that, bjornhall.

No one at my flight centre (one of the biggest in the UK, at that) were too excited about the problem. (Mind you if you told them the wings fell off they would just yawn):E

That C152 POH is fascinating. Is that based on the a real Cessna POH, Backpacker? It has a novel approach for controlling the aircraft if inadvertantly entering cloud -let go of the yoke and keep the little airplane in the turn co-ordinator level with the rudder. I'm going to try it on my next flight (not in cloud though)

Small mistake though (I think). When braking on a short runway it says push back on the stick - surely it should be forward? (Next action in the former case would be - apply full power - as the aircraft will be back in the sky!)

[worrab]

Pull back on the (yoke) to relieve some of the strain on the relatively fragile nosewheel assembly.

[SNS3Guppy]

It has a novel approach for controlling the aircraft if inadvertantly entering cloud -let go of the yoke and keep the little airplane in the turn co-ordinator level with the rudder.

Not too novel...this has been the standard counsel since prior to the second world war.

The concept is idiot proofing the maneuver, and trying to keep the pilot as much out of the process as possible. The pilot continues to be the most dangerous component in the aircraft, and it's the pilot who causes the loss of control in instrument conditions.

The safest counsel is to steer well clear of instrument conditions until you're properly trained, and thoroughly proficient. Inadvertant VFR into instrument conditions still continues to be a consistent killer of pilots and a destroyer of aircraft.

When braking on a short runway it says push back on the stick - surely it should be forward?

It should say pull back on the control yoke.

The bottom line with your aircraft, all other references is aside, is that it's not functioning properly. You need to refuse to fly it until it is functioning properly. There's no grey area. If the aircraft isn't right, don't fly. Period.

[Molesworth 1]

Not too novel...this has been the standard counsel since prior to the second world war.

No word of it in my PPL training that I recall. It's a great idea though - it's a pity it's not more widely taught as it could save lives.

[SNS3Guppy]

There's an enormous amount left out of training in that part of the world, from what I gather reading these posts. I'm quite amazed at the number of posters who suggest they've never been taught to properly lean an engine, or the proper use of carburetor heat...but these have been required knowledge for any student pilot from the very early days of flying.

What we have in flight training today is a heritage of inexperience. One low-time, inexperienced pilot teaching another. One pilot is taught by another who knows nothing more than what the low-time pilot before him taught when he got his first instructing job...it's a chain in which each up and coming instructor doesn't know or think for himself, but only repeats and rabbits what his own instructor did...and his own instructor did only what he was taught...ad nauseum.

Even today concepts such as ground effect being a cushion of air beneath the wing are still passed ignorantly from one instructor to another, taught to far too many students...when the truth is much more simple, and much more important to understanding flight.

In your Cessna 152, you may try another experiment some time. Run the trim full up with a power off descent, simulating a glide with the engine out to a landing...see what airspeed the airplane will hold in a glide. Then try it from level with power, trimmed hands off. Pull the power to idle with the trim given three full trims up (grasp the top of the wheel and pull it down to the bottom, three times). See what airspeed it holds. Somewhere between the two, closer to full up trim, you'll find that without any input from you, once trimmed, the airplane wants to glide all by itself. Then do the glide with rudders and see what happens.

This works great in calm conditions. Inside a cloud is very seldom calm. It's usually bumpy, and turbulent. The airplane doesn't want to stay wings level, and certainly doesn't want to hold a pitch attitude or an altitude. It doesn't want to maintain a stable descent, and it usually doesn't want to go straight. Add to this the illusions and disorientation that comes with entry or flight in the clouds, and you've got a recipe for disaster...hence the constant and urgent counsel to avoid flight in instrument conditions until properly certified and instructed.

[Gertrude the Wombat]

No word of it in my PPL training that I recall. It's a great idea though - it's a pity it's not more widely taught as it could save lives.
Perhaps TPTB think that even more lives could be saved by spending the time teaching "do not get into cloud, it will kill you" instead.

[BackPacker]

That C152 POH is fascinating. Is that based on the a real Cessna POH, Backpacker?

I honestly have no idea. It was the first or second Google hit and I only scanned it quickly until I found the 2550 number I was looking for. But I would assume that if someone goes to the trouble of summarizing a POH, that they would base it on the POH, yes.

What's more important to note is that the summary (or indeed a complete POH downloaded from the internet) may not be right for your model or even your specific airframe. So you should always verify the information with the actual POH of the actual aircraft.

Small mistake though (I think). When braking on a short runway it says push back on the stick - surely it should be forward?
Pull back on the (yoke) to relieve some of the strain on the relatively fragile nosewheel assembly.

Actually, for a short-field landing you pull back on the yoke/stick not to relieve stress on the nosewheel, but to put as much weight on the main wheels as possible. This allows for the most effective braking without skidding. Same reason you retract your flaps as soon as possible in such a situation: more weight on the wheels.

What you need to realize is that the main wheels are behind the center of gravity on an aircraft with a nosewheel. This means that anything that reduces the lift of the wings, or increases the downforce generated by the elevator, will increase the weight on the main wheels. And more weight on the main wheels means more effective directional control and more effective braking. In contrast, if you move the stick/yoke fully forward, the elevator will generate an up-force, effectively reducing the weight on the mainwheels.

There is a caveat though, which you rightfully pointed out. If you landed too fast and touched down with a speed above Vs, pulling back on the stick/yoke when still above Vs will normally result in getting airborne again. So for a short-field landing speed control on final is indeed critical and you should not attempt a short-field landing for real if you have any doubts about the ASI accuracy.

The bottom line with your aircraft, all other references is aside, is that it's not functioning properly. You need to refuse to fly it until it is functioning properly. There's no grey area. If the aircraft isn't right, don't fly. Period.

A few weeks ago I was preparing to fly from Rotterdam to Fenland for the aeros contest over there, but I was in serious doubts about being able to make it over the Channel, given the weather conditions and the equipment of the plane. A very experienced flight instructor told me: "Breathing and eating is mandatory or else you die. Paying taxes is mandatory because otherwise you'll be thrown in jail. Everything else is optional." Wise words.:ok:

[Molesworth 1]

for a short-field landing you pull back on the yoke/stick not to relieve stress on the nosewheel, but to put as much weight on the main wheels as possible


Thanks for the explanation, BackPacker - that makes complete sense.

[smarthawke]

I do hope that the rest of the machine is kept in finer fettle than that of the instrument panel condition...

With a potentially over-reading tacho or too fine a pitch prop on the front and it being flown in this condition without anyone seeming to care about your concerns make me think your money might be better spent at some other establishment.

Incidentally, all the C152 tachos I've seen/flow maintained have a green arc from 2000 - 2550 as the normal engine range of operation so the tacho fitted may be a 'non-genuine' one. Exactly what should infromation be displayed on the instrument panel, instruments and elsewhere on the airframe will be in the Placards section of the POH for that specifice aircraft (by registration/serial number not aircraft type).

[Molesworth 1]

I do hope that the rest of the machine is kept in finer fettle than that of the instrument panel condition...


Most of the rest of the plane is held together with duct tape:suspect::suspect::suspect:

[Pilot DAR]

What we have in flight training today is a heritage of inexperience.

Best line I've ever read on PPRuNe!

[Maoraigh1]

Trust your instructors. They will have preflighted it. They know the two basic parts of an aircraft:
The parts that are meant to move -if they don't, they'll have WD40'd them until they do.
The parts that are not meant to move - if they do move, they'll have duct tape them until they don't.

[Molesworth 1]

There's an enormous amount left out of training in that part of the world


Yes, but we know a great deal about the weather!:ooh:

[Big Pistons Forever]

Molesworth 1

I just saw the earlier post with the picture of your instrument panel. Why are you flying such a piece of ****e :confused: Surely there must be rental airplanes that don't look like crash scene photo's, available for rent.

[Final 3 Greens]

BigPistons

You would would be surprised at some of the wrecks that are rented out for big bucks in the UK.

[Final 3 Greens]

Molesworth

When you have sorted out a new and better self fly hire company, you may wish to write up this defect in the tech log using words to the effect "tachometer reading outside the permitted range, do not fly until rectified."

It won't win you any friends, but that's what is needed.

[Pilot DAR]

Yeah, I tend to agree with the remark about writing up planes with defects. That said, I rarely have. The reason being that I have never been in a stiuation where the operator of the plane was unwilling to rectify the defect as required (generally before the next flight, or at the next maintenance opportunity, as appropriate).

Assuring the safe flight of an aircraft is an attitude borne of a safe "culture". One indicator of that safe culture being in place is that a maintenance defect is rectified, or the aircraft grounded until it is. There are occasions where a flight would be undertaken with a known defect, but this would be with understanding of the defect, affect on the proposed flight, pilot skill, and the possible affect of changed conditions during the flight. Have I flown aircraft with defective primary instruments? Yes, but it was with full knowledge of the defect, and understanding how to safely work around it. There are "minor" defects which are just not worth the expense of rectifying on a lonely lake, 100 miles from anywhere.

But, that is not common to the general aviation rental environment. If you're simply renting a plane for an hour or two, you have a right to expect an aircraft which is airworthy for the intended flight. Yes, perhaps a nav light is not working, and not required for your planned day flight, but in that case, you are told that condition exists, so that you don't prolong your return into the night. But a tachometer should work right at all times - it is telling you about your operation of the aircraft relative to a limitaion of the operation!

So, be a courteous pilot first, and present your concern about a defect verbally if you can. If you are satisfied with the explanation, and are confident it will be addressed, you have held up your end of the safety culture responsibility. A write up might not be necessary, or might be done for you. If you doubt that anything will be done, then you should be writing it up, and looking for somewhere else to rent, where a better safety culture prevails. Writing up a defect as the first action should probably be reserved for situations where you are convinced that that is the only way to communicate the defect to the next pilot who might fly the plane. If you're taking that action, then a note in the instrument panel as a more "in your face" message, is also appropriate.

In the absence of a "Minimum Equipment List", which is not common to GA aircraft types, you, as the pilot are taking full responsibility for flying an aircraft with a defect known to you. It is your choice! No nav light for a day flight? Sure. No "wheel down" green light? No! It's the defect not known to you which is the problem for you, and responsibility of the preceding pilot, who suspected it, and did not assure that appropriate action was taken.

You're not going to crash a plane, because the tachometer does not work. But, there might be a much more serious accident one day, because someone else overspeeds the engine unknowingly, and then it later fails (by then, that tach could have been changed anyway!).

Airplanes generally don't crash because one thing was wrong, but when several little things wrong line up, you're at risk. They can line up wrong surprisingly quickly!

Pilot DAR