Chieftain Turbocharger run down times
Thread Starter
Chieftain Turbocharger run down times
The manufacturer recommends a "cool-down" time of three minutes at idle power after high power to aid cooling of the turbo-charger. Some operators set the throttles at 1000 rpm before engine shut-down, yet the manufacturer recommends idle rpm which is in the region of 650 rpm.
Surely if the point of the excercise is to cool down the turbines of the turbocharger until they stabilise at the lowest possible temperature, then seems to me that keeping the rpm at 1000 is defeating the purpose? Any comments?
Also some Chieftain operators maintain a minimum of 1200 rpm while taxying at night for battery charging with lights on etc and ride the brakes all the way out to the runway and all the way back to the tarmac to regulate the taxy speed at the higher rpm. Wouldn't this practice lead to hot brakes which might be needed in an abort? There is nothing in the manufacturer's POH about high rpm taxying to charge the battery so is it just another GA myth?
A Chieftain operator in Qld has brought in a requirement to check the magnetos at top of descent for dead cut at cruise power of 31MAP. While the mag switch is not switched off, the operator simply selects left then right magneto position to see if the engines runs OK. A dead mag will cause a big backfire and the theory is that delays on the ground can be anticipated and other arrangements made in plenty of time before the aircraft lands.
Again, there is no mention of this precautionary mag check in the manufacture's POH. I would have thought this was a potentially engine damaging procedure if done in flight if one magneto is proved to be dead and a large backfire is evident. Surely good airmanship would dictate that a check for dead cut is better left to after landing and back on the tarmac. Makes you wonder what CASA FOI's do for a living when this technique (airborne mag cut check) is apparently approved in the company Ops Manual.
Surely if the point of the excercise is to cool down the turbines of the turbocharger until they stabilise at the lowest possible temperature, then seems to me that keeping the rpm at 1000 is defeating the purpose? Any comments?
Also some Chieftain operators maintain a minimum of 1200 rpm while taxying at night for battery charging with lights on etc and ride the brakes all the way out to the runway and all the way back to the tarmac to regulate the taxy speed at the higher rpm. Wouldn't this practice lead to hot brakes which might be needed in an abort? There is nothing in the manufacturer's POH about high rpm taxying to charge the battery so is it just another GA myth?
A Chieftain operator in Qld has brought in a requirement to check the magnetos at top of descent for dead cut at cruise power of 31MAP. While the mag switch is not switched off, the operator simply selects left then right magneto position to see if the engines runs OK. A dead mag will cause a big backfire and the theory is that delays on the ground can be anticipated and other arrangements made in plenty of time before the aircraft lands.
Again, there is no mention of this precautionary mag check in the manufacture's POH. I would have thought this was a potentially engine damaging procedure if done in flight if one magneto is proved to be dead and a large backfire is evident. Surely good airmanship would dictate that a check for dead cut is better left to after landing and back on the tarmac. Makes you wonder what CASA FOI's do for a living when this technique (airborne mag cut check) is apparently approved in the company Ops Manual.
Last edited by Centaurus; 21st Sep 2005 at 07:47.
Centaurus you've hit on an interesting an often misunderstood issue. The amount of increase in boost the turbo delivers at even 1000rpm (versus say 650rpm) is almost nothing (certainly in the region of less than half an inch MAP due lag and blade efficiency). There would of course be an increase in cooling airflow through both sides of the turbo at 1000rpm and a corresponding increase in oil pressure (therefore cooling oil flow through the turbo) at the higher idle rpm.
The issue isn't to remove all of the temperature from the unit, it is to stabilise the temps to a more even (read: no hotspots) temperature within the unit. The idea is to remove the workload from the engine enough to temp stabilise it to a dull roar. Some POH's for the aircraft also make mention of EGT's to be below a certain temperature also before shutdown in addition to the time requirement. Sustained lower rpm may also lead to fouling.
Alternators also rely upon more RPM to provide a higher amperage so satisfy any current draw load that the pilot has set them the task of satisfying. Personally, I wouldn't use 1200rpm to taxi at night unless I was climbing a steepish taxiway such as at Darwin. Have flown the chief (albeit a while ago), but have many more hours in the C402 so cannot really comment on the 1200rpm except to say that that if I were paying the bills I wouldn't be keen on it.
OpsN.
The issue isn't to remove all of the temperature from the unit, it is to stabilise the temps to a more even (read: no hotspots) temperature within the unit. The idea is to remove the workload from the engine enough to temp stabilise it to a dull roar. Some POH's for the aircraft also make mention of EGT's to be below a certain temperature also before shutdown in addition to the time requirement. Sustained lower rpm may also lead to fouling.
Alternators also rely upon more RPM to provide a higher amperage so satisfy any current draw load that the pilot has set them the task of satisfying. Personally, I wouldn't use 1200rpm to taxi at night unless I was climbing a steepish taxiway such as at Darwin. Have flown the chief (albeit a while ago), but have many more hours in the C402 so cannot really comment on the 1200rpm except to say that that if I were paying the bills I wouldn't be keen on it.
OpsN.
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In theory the idle RPM should be set at about 650-700 RPM, in reality I find its usually about 850-1000 RPM. My basic run down procedure is to idle the engines for about 3 mins at the lowest RPM that they will run stable at, check that the EGT is below 800 degrees, then shut down. Running the 'Hi' fuel pumps during cool down will also lower the RPM by about another 50-100 RPM.
The mag check at TOD is a useless and perhaps even dangerous idea, I've had 2 mag failures in flight in Navajo/Chieftains and trust me you notice them, symptoms include slightly rough running, a small RPM drop and a rise in EGT, all of which are
noticable during standard CLEAROFF checks, thus no need to do a mag check at all during flight... would be VERY surprised if that crap was in an ops manual.
As for taxing at 1200 RPM... not a standard operating procedure. I often fly night ops in the Chieftain and have never had a situation where I have run low on electrical power or flattened the battery during taxi, just operate as you would normally duing
any other flight.
In short, every operator has different procedures, my advice is to listen to all the available advice/theories then adopt what works best for you (With-in the bounds of the company ops manual, of course)
The mag check at TOD is a useless and perhaps even dangerous idea, I've had 2 mag failures in flight in Navajo/Chieftains and trust me you notice them, symptoms include slightly rough running, a small RPM drop and a rise in EGT, all of which are
noticable during standard CLEAROFF checks, thus no need to do a mag check at all during flight... would be VERY surprised if that crap was in an ops manual.
As for taxing at 1200 RPM... not a standard operating procedure. I often fly night ops in the Chieftain and have never had a situation where I have run low on electrical power or flattened the battery during taxi, just operate as you would normally duing
any other flight.
In short, every operator has different procedures, my advice is to listen to all the available advice/theories then adopt what works best for you (With-in the bounds of the company ops manual, of course)
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A Chieftain operator in Qld has brought in a requirement to check the magnetos at top of descent for dead cut at cruise power of 31MAP. While the mag switch is not switched off, the operator simply selects left then right magneto position to see if the engines runs OK.
Why, oh why, do operators and pilots think they are enhancing safety by introducing procedures which are not approved by the manufacturer???????? Do you think these manufacturers don't know their own product?
Centaurus, you answered your own question: "The manufacturer recommends a "cool-down" time of three minutes at idle power after high power to aid cooling of the turbo-charger." Why are you seeking to implement or obtain opinions on procedures which may be contrary to the manufacturer's recommendation?
Perhaps I should change the title of this thread to "What non standard procedures can we introduce"?
Woomera
Last edited by Woomera; 21st Sep 2005 at 10:08.
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Cplane. I suspected the alternator gearing would be adequate to sustain power load in taxi, regardless of whether day or night power loading. Just didn't want to make a goose of myself!
So now we have pilots and operators again re-inventing the wheel - and wearing brake pads into the bargain.
The aircraft POH should be required reading for anyone considering launching forth. I wonder why pilots and operators won't read it?
Woomera
So now we have pilots and operators again re-inventing the wheel - and wearing brake pads into the bargain.
The aircraft POH should be required reading for anyone considering launching forth. I wonder why pilots and operators won't read it?
Woomera
I would not presume to misrepresent that I have anywhere near the experience of the earlier posters on this thread with respect to the question that’s been asked, but I do note the different but perhaps analogous debate about lean-of-peak operations. There aren’t too many POHs or erstwhile flight manuals that permit or permitted lean-of-peak operations, yet folks like Mr Deakin have been scathingly critical of that fact. More importantly, they have provided objective evidence in support of LOP ops. Mr Deakin is probably comforted (though he probably didn’t need to be comforted) by the fact that those ‘old’ engines in ‘modern’ FADEC-equipped aircraft automatically and deliberately operate LOP.
I suppose my point is that just because something’s not recommended or included in an aircraft manufacturer’s manual, it does not necessarily follow that it’s not a safe or good idea.
That said, the thing to do is separate the facts from the fiction. For example, the RPM at which generator/s/alternator/s is/are capable of putting out more power than is being consumed by the total load imposed by live aircraft systems, is determined by the laws of physics, not opinion. If the generator/s/alternator/s is/are capable of delivering the required power at idle RPM, the next question is the point at which the voltage regulator switches over – another question of fact, not opinion.
Perhaps the output of the generator/s/alternator/s is very dirty and lumpy at low RPM, even though the load could be borne in theory, thus causing damage to those oh-so-modern GA avionics in practice.
I suppose my point is that just because something’s not recommended or included in an aircraft manufacturer’s manual, it does not necessarily follow that it’s not a safe or good idea.
That said, the thing to do is separate the facts from the fiction. For example, the RPM at which generator/s/alternator/s is/are capable of putting out more power than is being consumed by the total load imposed by live aircraft systems, is determined by the laws of physics, not opinion. If the generator/s/alternator/s is/are capable of delivering the required power at idle RPM, the next question is the point at which the voltage regulator switches over – another question of fact, not opinion.
Perhaps the output of the generator/s/alternator/s is very dirty and lumpy at low RPM, even though the load could be borne in theory, thus causing damage to those oh-so-modern GA avionics in practice.
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what I find really amazing is when pilots land at ,say YSBK, and SLAM on the brakes to take first possible taxiway - and beat their mates to the freight shed - then sit there with engines at idle for three more minutes!Why not just roll to the end (traffic permitting) then a leisurely taxi to the freight shed at IDLE, and shut down straight away ?(presuming it has cooled down the three minutes)
An engineer mate once told me also, that the Turbines are NOT working below 25in.hg, hence if you hit the circuit at say 22in.hg, and get down at 22 or below, then taxi, then the cool down time has been achieved. Is this not true ? Let's face it, when applying power for take-off, the turbines only cut in at about 2500RPM/25IN HG.
My theory has alweays been to do what the OPERATOR states that he/she wants you to do (within reason) - which is NORMALLY exactly what the POH says to do - and then IF there is a problem, then YOUR ARS# is covered!
An engineer mate once told me also, that the Turbines are NOT working below 25in.hg, hence if you hit the circuit at say 22in.hg, and get down at 22 or below, then taxi, then the cool down time has been achieved. Is this not true ? Let's face it, when applying power for take-off, the turbines only cut in at about 2500RPM/25IN HG.
My theory has alweays been to do what the OPERATOR states that he/she wants you to do (within reason) - which is NORMALLY exactly what the POH says to do - and then IF there is a problem, then YOUR ARS# is covered!
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check that the EGT is below 800 degrees
It's been a while since I flew a Chieftain, but some of the stuff Centaurus is mentioning seems too OTT.
1. 1200rpm taxi with brakes is definitely unnecessary. I flew them mostly night operations and never had problems with having enough electrical power at taxi at normal taxi rpm. Putting all that heat into the brakes, even with the BIG brakes option is pointless.
What happens in the event of an aborted TKO, or worse, and EFATO still below blue line?
At ANY speed below blue line, and that bird ain't gonna fly, so a re-land is the only option, and you're gonna need every single bit of brake energy to ensure that you hit the fence at the end of the runway at the lowest opossible GS.
2. Mag check at cruise power is unnecessary. The mags were checked during run-ups, right? So they should be working fine. If a magneto does fail inflight, it will be noticeable. This sort of excercise airborne for the sake of 'schedule integrity' risks engine damage and subsequent urgency/emergency situation, and introduces a risk to the safe outcome of the flight - unnecessarily.
3. The turbochargers, if my memory serves me correctly, are not really on boost at pwer setting of 24" MAP or less. Typical power settings in the circuit range from about 18"MAP to 24"MAP depending on AUW and position (downwind or base/final). A 3 minute dwell time after landing is appropriate, and more if excessive power was used for the landing (eg correcting for below GS or low approach).
You hear of so many 'voodoo' methods of operating Chieftains, it can really be incredulous. I would be surprised that CASA are approving such procedures as mentioned by Centaurus that have no basis in manufacturer's data or procedures.
If they are approving this, what the hell are they doing???
PS Creamy, As far as I understand, the L.O.P procedures that Deakin advocates are in combination with aftermarket EGT gauges (using egt probes on individual cylinders) and (GAMI) Injectors. Standard EGT gauges are not accurate enough and do not measure EGT at each cylinder. Also, from memory, the LOP stuff was for normally aspirated engines, not turbocharged (but i could be incorrect on the last matter).
Thread Starter
I may be wrong, but I have the impression that CASA will "approve" (if that is the right word) anything as long as it published in the company operations manual. The procedure may not necessarily be in the manufacturer's POH or may differ from the POH, but as long as it is written in the Operations Manual where CASA can nail you if things go wrong, then that satisfies most FOI's.
The book by Kas Thomas called "Fly the Engine" has this to say about run-down times. If you haven't read the book, it is (was?) available at pilot shops and he also wrote Personal Aircraft Maintenance (1981), Aircraft Engine Operating Guide (1985), EGT Systems (1989), and The Major Overhaul (1994).
Face into wind and keep the engine running. Don't be in a hurry to shut a turbocharged engine down..always idle 4 to 7 minutes (depending on OAT) facing into wind to allow circulating oil to carry away heat from the turbocharging bearing housing.
Idling I suppose is just that - the book says the engines should idle 650-750 rpm. Woomera, by the way..I don't fly Chieftains so don't blame me for the instances that I have noted in my original post. These are purely discussion areas. And as for someone saying that all company Ops Manuals agree with recommendations published in POH - don't you believe it.
The book by Kas Thomas called "Fly the Engine" has this to say about run-down times. If you haven't read the book, it is (was?) available at pilot shops and he also wrote Personal Aircraft Maintenance (1981), Aircraft Engine Operating Guide (1985), EGT Systems (1989), and The Major Overhaul (1994).
Face into wind and keep the engine running. Don't be in a hurry to shut a turbocharged engine down..always idle 4 to 7 minutes (depending on OAT) facing into wind to allow circulating oil to carry away heat from the turbocharging bearing housing.
Idling I suppose is just that - the book says the engines should idle 650-750 rpm. Woomera, by the way..I don't fly Chieftains so don't blame me for the instances that I have noted in my original post. These are purely discussion areas. And as for someone saying that all company Ops Manuals agree with recommendations published in POH - don't you believe it.
This article from John Deakin will sort out any arguments.
Its funny to listen to pilots perpetuating old wives tales after flying aircraft with rudimentry or no instrumentation at all. truth is, most dont know what they are talking about because there is no way of telling exactly what is actually going on inside the engine.
Better yet, anyone who realy wants to learn how to operate these engines should attent the advanced pilots seminar run by John deaken in the US where u get to operate a chieftain engine in the worlds most advanced test cell and you can see what is really happening.
http://www.avweb.com/news/columns/182107-1.html
http://www.advancedpilot.com/course.html
Its funny to listen to pilots perpetuating old wives tales after flying aircraft with rudimentry or no instrumentation at all. truth is, most dont know what they are talking about because there is no way of telling exactly what is actually going on inside the engine.
Better yet, anyone who realy wants to learn how to operate these engines should attent the advanced pilots seminar run by John deaken in the US where u get to operate a chieftain engine in the worlds most advanced test cell and you can see what is really happening.
http://www.avweb.com/news/columns/182107-1.html
http://www.advancedpilot.com/course.html
Jet-A: spot on re your comments on the instrumentation and matched injectors that usually go with LOP. They mean you can actually know that you’re there. Turbo or normally aspirated – doesn’t make a difference, and Deakin explains why. How the fuel and the air gets mixed makes no difference to the performance/temperature/lean curves.
The funny thing is that just as a single, inaccurate egt gauge won’t tell us whether all of the cylinders are running LOP, it won’t tell us whether all of them are running ROP either! As Deakin shows, the ‘spread’ of fuel flows and corresponding EGTs can be very large across cylinders. Consequently and ironically, those who diligently tweak that egt gauge ROP might not have all cylinders there.
The old POHs should not say “LOP operations are not recommended”. They should say “There are some very good ways of getting your engine to run at its best, but we haven’t fitted the instruments for you to know if you are. Consequently, we’d like to hedge our risk by getting you to use that cheap AVGAS stuff to keep our cylinders cool – thanks.”
Nomorecatering’s links are in my view essential reading for anyone who runs squash bang engines.
The funny thing is that just as a single, inaccurate egt gauge won’t tell us whether all of the cylinders are running LOP, it won’t tell us whether all of them are running ROP either! As Deakin shows, the ‘spread’ of fuel flows and corresponding EGTs can be very large across cylinders. Consequently and ironically, those who diligently tweak that egt gauge ROP might not have all cylinders there.
The old POHs should not say “LOP operations are not recommended”. They should say “There are some very good ways of getting your engine to run at its best, but we haven’t fitted the instruments for you to know if you are. Consequently, we’d like to hedge our risk by getting you to use that cheap AVGAS stuff to keep our cylinders cool – thanks.”
Nomorecatering’s links are in my view essential reading for anyone who runs squash bang engines.
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Centaurus does raise a few issues that I also have seen first hand. Riding brakes is common, and pointless, and quite probably detrimental if you have to do that abort. Just like any larger a/c, they were designed for one emergency stop, (and marginal at that, especially if your Chieftain has the poverty pack brakes). How many times do you see pilots taxi in with strobes, BOTH landing and taxi lights on, pitot heat on etc. No wonder the alternators can't keep up at low RPM. In 5 years I've never seen a flattened battery taxiing a Chieftain at night yet.
Jet- A, 800 degrees is correct for EGT. Haven't yet seen a Chieftain EGT gauge calibrated in celcius. Most gauges I've seen have as a minimum 800 or 900 degrees fahrenheit.
Centaurus, you are correct about the Ops Manual simply containing whatever you want these days. Having been through the process recently, they will approve pretty much whatever you want to put in there. As they say though, "Be careful what you wish for", as they WILL hang you with it later if someone F%*&S up..........
Jet- A, 800 degrees is correct for EGT. Haven't yet seen a Chieftain EGT gauge calibrated in celcius. Most gauges I've seen have as a minimum 800 or 900 degrees fahrenheit.
Centaurus, you are correct about the Ops Manual simply containing whatever you want these days. Having been through the process recently, they will approve pretty much whatever you want to put in there. As they say though, "Be careful what you wish for", as they WILL hang you with it later if someone F%*&S up..........
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Cool down time 3 mins after exiting the runway and 5 minutes if I have just done a go-around worked for me.
A couple of years ago, I was at a strip and a dude was coming and going in a Navajo. The taxiway was straight off the end with a 50 metre taxy. My mate and I asked this dude after a while why he would taxi straight in, not cool down and shutdown. He didn't really seem to know what we were talking about in regards to turbo cooling. He had been doing this for a year and had not had any turbo problems (apparently??).
What the ...?
A couple of years ago, I was at a strip and a dude was coming and going in a Navajo. The taxiway was straight off the end with a 50 metre taxy. My mate and I asked this dude after a while why he would taxi straight in, not cool down and shutdown. He didn't really seem to know what we were talking about in regards to turbo cooling. He had been doing this for a year and had not had any turbo problems (apparently??).
What the ...?
Boney,
If hes using the right approach technique, and already has cylinder head temps of around 300 deg F and using a low manifold pressure, the turbo will be cooling down during the approach. In this case a long taxy, cooldown period will only make the cylinder head temps rise.
Excerpt from John Deakins "Those Fire Breathing Turbos Pt 6"
Cooldown/Shutdown
I would guess that when you see (and hear!) someone running their engine in the parking spot after landing "to cool the turbo," you are almost always seeing someone who is getting it hotter than it was when he arrived at the spot. If you don't make the high-drag approaches, and you lean brutally after landing, that turbo will be just about as cold as it will ever get, short of a shutdown. On the other hand, if you've made a long, high-drag approach with high power, or you're one of those dreadful types who taxi with cruise power while dragging the brakes to keep the speed down, or you have a long, sharply uphill taxi to the ramp, you may need the cool down. A tip that might do your engine more good is to hop right out after shutdown, and pop the cowling open (or even just the oil access door) if you can. That will let a LOT of heat out of the accessory section, avoiding "cooking" the components, hoses, and seals there. But even that little tip is probably completely unnecessary if there is more than 3-5 knots of wind blowing in the general direction of either the front or the back (cowl flaps open, please) of the engine.
George Braly again:
We know of one operator of a turbo twin Cessna. He owned the aircraft for 15 years before the issue of "turbo cool down" ever showed up in the aviation literature. Through three full TBO runs, with almost no premature engine or turbo problems, this operator would routinely land at his uncontrolled airport, turn off at mid-field, taxi about 100 yards, and immediately shut down both engines. The aircraft was then promptly pushed into a T-hangar, where it could not benefit from any natural wind for a further cool down. These would have been ideal conditions to promote problems with turbochargers not being properly allowed to cool down, if there was any truth to this OWT. This operator, in more than 8000 engine hours, never experienced any problems with the issue of "coking" a bearing on a turbocharger.
Finally, here's a graph of the type of descent I've just described.
Click for a high-resolution version.
The chart begins at 11:49:21 PDT, on 10/02/2000, at 10,500 feet. Note that TIT and EGT is read against the left side numbers, while all other parameters are read against the right side. For the first five minutes, I pre-cool the CHTs by beginning a gentle descent, and reducing RPM and fuel flow on the lean side. That CHT drop too fast for you? Fine, you have complete control over how fast you drop the CHTs, take all the time you want.
At about 11:55:00, I simply pulled the throttle back, and dropped the MP from 31.0" to 18.0". In order to demonstrate where the mixture ended up to a passenger, I fiddled with it a bit, and added just a bit of fuel. In fact, it would probably have been better if I'd just left it alone (as I usually do) because that extra tweak actually caused the CHTs and EGTs to RISE! Uhh, what WERE you saying about "shock cooling"? We have just pulled off 12 full inches of MP in one swell foop, and all engine temps go UP! The reason is, of course, we have gone from very LOP (and relatively cool CHTs) at a very high power setting, to just ROP at a very low setting. The linkages in my engine are "just right" for this purpose, yours may vary, but at worst, you'll need to fiddle with the mixture once, to get it just ROP, or wherever you want it.
For the next 10 minutes on the chart, we descend at about 1,000 fpm, at about 140 knots, gear up. If I'd wanted more descent, all I had to do was run the IAS up to the bottom of the yellow arc, or put the gear down, or even pull off more MP. For a couple minutes in the pattern, the CHTs dropped very gently and then they rise a bit while taxiing in. At shutdown, they begin a long, slow cooling process.
Well, we've gone from startup to shutdown, with a "flight time" of five months! I hope I've not led you too far astray, and above all, I hope I've made you think.
I think I'll take a break from engines, for a while!
Be careful up there!
If hes using the right approach technique, and already has cylinder head temps of around 300 deg F and using a low manifold pressure, the turbo will be cooling down during the approach. In this case a long taxy, cooldown period will only make the cylinder head temps rise.
Excerpt from John Deakins "Those Fire Breathing Turbos Pt 6"
Cooldown/Shutdown
I would guess that when you see (and hear!) someone running their engine in the parking spot after landing "to cool the turbo," you are almost always seeing someone who is getting it hotter than it was when he arrived at the spot. If you don't make the high-drag approaches, and you lean brutally after landing, that turbo will be just about as cold as it will ever get, short of a shutdown. On the other hand, if you've made a long, high-drag approach with high power, or you're one of those dreadful types who taxi with cruise power while dragging the brakes to keep the speed down, or you have a long, sharply uphill taxi to the ramp, you may need the cool down. A tip that might do your engine more good is to hop right out after shutdown, and pop the cowling open (or even just the oil access door) if you can. That will let a LOT of heat out of the accessory section, avoiding "cooking" the components, hoses, and seals there. But even that little tip is probably completely unnecessary if there is more than 3-5 knots of wind blowing in the general direction of either the front or the back (cowl flaps open, please) of the engine.
George Braly again:
We know of one operator of a turbo twin Cessna. He owned the aircraft for 15 years before the issue of "turbo cool down" ever showed up in the aviation literature. Through three full TBO runs, with almost no premature engine or turbo problems, this operator would routinely land at his uncontrolled airport, turn off at mid-field, taxi about 100 yards, and immediately shut down both engines. The aircraft was then promptly pushed into a T-hangar, where it could not benefit from any natural wind for a further cool down. These would have been ideal conditions to promote problems with turbochargers not being properly allowed to cool down, if there was any truth to this OWT. This operator, in more than 8000 engine hours, never experienced any problems with the issue of "coking" a bearing on a turbocharger.
Finally, here's a graph of the type of descent I've just described.
Click for a high-resolution version.
The chart begins at 11:49:21 PDT, on 10/02/2000, at 10,500 feet. Note that TIT and EGT is read against the left side numbers, while all other parameters are read against the right side. For the first five minutes, I pre-cool the CHTs by beginning a gentle descent, and reducing RPM and fuel flow on the lean side. That CHT drop too fast for you? Fine, you have complete control over how fast you drop the CHTs, take all the time you want.
At about 11:55:00, I simply pulled the throttle back, and dropped the MP from 31.0" to 18.0". In order to demonstrate where the mixture ended up to a passenger, I fiddled with it a bit, and added just a bit of fuel. In fact, it would probably have been better if I'd just left it alone (as I usually do) because that extra tweak actually caused the CHTs and EGTs to RISE! Uhh, what WERE you saying about "shock cooling"? We have just pulled off 12 full inches of MP in one swell foop, and all engine temps go UP! The reason is, of course, we have gone from very LOP (and relatively cool CHTs) at a very high power setting, to just ROP at a very low setting. The linkages in my engine are "just right" for this purpose, yours may vary, but at worst, you'll need to fiddle with the mixture once, to get it just ROP, or wherever you want it.
For the next 10 minutes on the chart, we descend at about 1,000 fpm, at about 140 knots, gear up. If I'd wanted more descent, all I had to do was run the IAS up to the bottom of the yellow arc, or put the gear down, or even pull off more MP. For a couple minutes in the pattern, the CHTs dropped very gently and then they rise a bit while taxiing in. At shutdown, they begin a long, slow cooling process.
Well, we've gone from startup to shutdown, with a "flight time" of five months! I hope I've not led you too far astray, and above all, I hope I've made you think.
I think I'll take a break from engines, for a while!
Be careful up there!
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Creampuff says, correctly;
Unless you have "the instruments" the argument is academic.
Others including Jet_A_Knight get the time/temp message.
It's the time since you had any power sufficient to "work" the turbos that is significant not the time on the ground, i.e. if you get your profile right that could mean from way back in the descent somewhere or when you had to rescue the landing with big burst.
AND
Stabilised CHT/EGT temps circa 300 deg F or whatever.
Anything else, as Woomera says, outside the POH is just the usual aero club bar/guru nonsense.
Oh and CASA "approved" pretty much follows the old IT mantra, sh!t in = sh!t out.
Some moons ago I had an urgent call from a distraught mining comany Managing Director, whose staff had just been involved in the closest thing to death they would likely ever experience, simultaneously with a CAA FOI, both asking how much fuel would be required blah blah to complete a specific flight and the load available, blah blah.
It took me less than 2 minutes to give em the result, shocked silence from both.......then the ususal "that can't be right"
.......followed by ...."well you asked the question if you already knew the answer why bother" followed by...."why do you ask". The firies were still cleaning up the mess at Perth.
C421C, aircraft departs with 10 POB (9 x 100kg drillers) and toolboxes for around 600nm direct flight inbound to Perth, suffers failure of remaining alternator, the other had failed outbound, dodgy to nonexistent coms for the last two thirds of the flight, overflys no less than 4 perfectly adequate strips with fuel, runs out of fuel on short finals and lands wheels up. No physical injuries but many of the passengers required long term counselling and would, not surprisingly, refuse any further FIFO work.
If one knows the approach to R24 then one can only contemplate the horrors and inevitable consequences of a dead stick into the hills prior.
Believe it or not = TRUE.
How?? Dodgy Bros charter company wins work against bona fide competitor due price and "ability" to operate non stop with the "same" load in the same type albeit with dodgy maintenance, sounding familiar no.
The "load chart" was "approved" using 77kg std pax, the operator was double dipping the 4 kg hand baggage allowance included in the std pax weight to lay of against the real baggage and so on. Hey these kids should get to run Telstra
The "approved" fuel flows and flight planning fuels were fantasy land and must have been worked back from the dodgy pax and freight weights to "balance out".
There was no POH or power computer on board beyond the CAA Flight Manual with the weights etc.
No mention anywhere in the OPs Manual of alternator failure issues and so on.
All duly "approved".
The outbound alternator failure on it's own is normally cause to ground the aircraft and other arrangements made for the pax.
Of course when the whole load is then put on the remaining equally old alternator for the return it promptly says barlees and rolls over shortly after TO on climb outbound and the battery is following fast.
Our hero decides no biggie
its sorta VFR daytime so lets keep going, we can't afford to put the pax on the RPT nor recover the aircraft from 600nm from base, so lets just keep going and make it up as we go along.
Now if the pilot in the stress and confusion had remembered to complete his checklists and properly leaned for the climb and cruise and not left it at full rich he may well have made it. Which is why he ran out of fuel at the vinegar stroke.
Now, a short lesson on geared engines and geared alternators. There's several ways an alternator can fail on one of these, internal electrical fault, internal bearing/shaft failure or failure at the gearbox end.
There is no way of telling from the cockpit other than it's offline.
For all but the first instance, alternator failure can have knock on consequences to the engine by taking out the gearbox, to which the engine and prop is attached altogether.
Not pretty.
Recommended practise is to land real soon and call the RAC.
But hey, now we have the hero flying an aircraft with BOTH alternators out.
Back to our hero, we are now well and truly into our fixed reserves and likely to land on fumes as we pass overhead the last airport with fuel, but hey even that is too expensive so lets keep going.
Mental state of the pilot is exhibited by the pax in the RHS decamping to the rear baggage step, which wouldn't have helped the C o G but I guess that was sorta offset by the 110kg tool box in the nose.
This was one of the pax who required big time counselling
Engines spluttering on short final, shut down one, I think, the other threatening, it might have given up too, stuff up gear extension, no hydraulics and emergency extension, fails to pull the gear breaker before selecting blow down and he does the only smart thing in the whole flight.
He dead sticks the aircraft more or less under control, gear hanging unlocked onto the ground
With the possible exception of the alternator issues all of the rest in terms of fuel and load were as per the "approved" Ops Manual.
I've the forgotten the denouement in terms of regulatory action but it was a bit of a stand off in finding any operations that weren't specifically approved and I seem to recall every body called it quits.
Fortunately for the industry Dodgy Bros went broke or went on to bigger things in airlines and the CAA learnt that the factory POH is remarkably accurate, as when I was eventually apprised of the actual fuel on board and other bits of the scenario I was able to show that the engines would quit pretty much on schedule and where they ultimately did. It wasn't rocket science.
AND that even with proper fuel handling they must have been landing with less than 30 minutes fuel, AND any way they cut it they were always 100s of kg overweight.
The POH and power computer probably were as is usually the case in the Chief Pilots top drawer, consigned as manufacturers puff advertising material.
Luck seems to favour the innocent.
The old POHs should not say “LOP operations are not recommended”. They should say “There are some very good ways of getting your engine to run at its best, but we haven’t fitted the instruments for you to know if you are. Consequently, we’d like to hedge our risk by getting you to use that cheap AVGAS stuff to keep our cylinders cool – thanks.”
Unless you have "the instruments" the argument is academic.
Others including Jet_A_Knight get the time/temp message.
It's the time since you had any power sufficient to "work" the turbos that is significant not the time on the ground, i.e. if you get your profile right that could mean from way back in the descent somewhere or when you had to rescue the landing with big burst.
AND
Stabilised CHT/EGT temps circa 300 deg F or whatever.
Anything else, as Woomera says, outside the POH is just the usual aero club bar/guru nonsense.
Oh and CASA "approved" pretty much follows the old IT mantra, sh!t in = sh!t out.
Some moons ago I had an urgent call from a distraught mining comany Managing Director, whose staff had just been involved in the closest thing to death they would likely ever experience, simultaneously with a CAA FOI, both asking how much fuel would be required blah blah to complete a specific flight and the load available, blah blah.
It took me less than 2 minutes to give em the result, shocked silence from both.......then the ususal "that can't be right"
.......followed by ...."well you asked the question if you already knew the answer why bother" followed by...."why do you ask". The firies were still cleaning up the mess at Perth.C421C, aircraft departs with 10 POB (9 x 100kg drillers) and toolboxes for around 600nm direct flight inbound to Perth, suffers failure of remaining alternator, the other had failed outbound, dodgy to nonexistent coms for the last two thirds of the flight, overflys no less than 4 perfectly adequate strips with fuel, runs out of fuel on short finals and lands wheels up. No physical injuries but many of the passengers required long term counselling and would, not surprisingly, refuse any further FIFO work.
If one knows the approach to R24 then one can only contemplate the horrors and inevitable consequences of a dead stick into the hills prior.
Believe it or not = TRUE.
How?? Dodgy Bros charter company wins work against bona fide competitor due price and "ability" to operate non stop with the "same" load in the same type albeit with dodgy maintenance, sounding familiar no.
The "load chart" was "approved" using 77kg std pax, the operator was double dipping the 4 kg hand baggage allowance included in the std pax weight to lay of against the real baggage and so on. Hey these kids should get to run Telstra
The "approved" fuel flows and flight planning fuels were fantasy land and must have been worked back from the dodgy pax and freight weights to "balance out".
There was no POH or power computer on board beyond the CAA Flight Manual with the weights etc.
No mention anywhere in the OPs Manual of alternator failure issues and so on.
All duly "approved".
The outbound alternator failure on it's own is normally cause to ground the aircraft and other arrangements made for the pax.
Of course when the whole load is then put on the remaining equally old alternator for the return it promptly says barlees and rolls over shortly after TO on climb outbound and the battery is following fast.
Our hero decides no biggie
its sorta VFR daytime so lets keep going, we can't afford to put the pax on the RPT nor recover the aircraft from 600nm from base, so lets just keep going and make it up as we go along.Now if the pilot in the stress and confusion had remembered to complete his checklists and properly leaned for the climb and cruise and not left it at full rich he may well have made it. Which is why he ran out of fuel at the vinegar stroke.
Now, a short lesson on geared engines and geared alternators. There's several ways an alternator can fail on one of these, internal electrical fault, internal bearing/shaft failure or failure at the gearbox end.
There is no way of telling from the cockpit other than it's offline.
For all but the first instance, alternator failure can have knock on consequences to the engine by taking out the gearbox, to which the engine and prop is attached altogether.
Not pretty.
Recommended practise is to land real soon and call the RAC.
But hey, now we have the hero flying an aircraft with BOTH alternators out.
Back to our hero, we are now well and truly into our fixed reserves and likely to land on fumes as we pass overhead the last airport with fuel, but hey even that is too expensive so lets keep going.
Mental state of the pilot is exhibited by the pax in the RHS decamping to the rear baggage step, which wouldn't have helped the C o G but I guess that was sorta offset by the 110kg tool box in the nose.
This was one of the pax who required big time counsellingEngines spluttering on short final, shut down one, I think, the other threatening, it might have given up too, stuff up gear extension, no hydraulics and emergency extension, fails to pull the gear breaker before selecting blow down
and he does the only smart thing in the whole flight.He dead sticks the aircraft more or less under control, gear hanging unlocked onto the ground
With the possible exception of the alternator issues all of the rest in terms of fuel and load were as per the "approved" Ops Manual.
I've the forgotten the denouement in terms of regulatory action but it was a bit of a stand off in finding any operations that weren't specifically approved
and I seem to recall every body called it quits.Fortunately for the industry Dodgy Bros went broke or went on to bigger things in airlines and the CAA learnt that the factory POH is remarkably accurate, as when I was eventually apprised of the actual fuel on board and other bits of the scenario I was able to show that the engines would quit pretty much on schedule and where they ultimately did. It wasn't rocket science.
AND that even with proper fuel handling they must have been landing with less than 30 minutes fuel, AND any way they cut it they were always 100s of kg overweight.
The POH and power computer probably were as is usually the case in the Chief Pilots top drawer, consigned as manufacturers puff advertising material.
Luck seems to favour the innocent.
Last edited by gaunty; 22nd Sep 2005 at 05:04.
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Creampuff - thanks for pointing out the relevance of Deakin's LOP ops for turbos - it's been a while since I read those articles.
Gaunty - A truly amazing story, which brings to light (amongst the stupidity of it all) another problem with many pilots: Their lack UNDERSTANDING of the systems, and their inter-relationships.
It's one thing to 'know' the systems, it's another to actually understand it.
In their (sort of defence) you can't always blame the pilot for not having the depth of understanding of the 'machine'. The typical CASA engineering quiz that one does when doing a type endorsement is not detailed enough, in my opinion, and gaining access to aircraft engineering manuals &/or parts catalogues, is a difficult excercise and one has to actively seek out sympathetic engineers ormaintenance organisations in order to 'borrow' and copy pertinent parts of those manuals.
Personally, I always strived to get an engineers' type understanding of the machine and its parts - not that I could fix it airborne (or on the ground) - but that level of understanding allowed me to spot developing, or actual, problems and communicate those problems more effectively to the LAME's to give them a better chance at troubleshooting, fault finding & fixing the problem. That helped me maintain my schedule integrity, inform operations of foreseeable problems so they can re-plan things or get an effective rescue going early on in the piece - without comprimising safety.
When you know and understand the machine, you realise what a load of bollocks some of the pointlessly crazy stunts people pull with these aeroplanes.
Gaunty - A truly amazing story, which brings to light (amongst the stupidity of it all) another problem with many pilots: Their lack UNDERSTANDING of the systems, and their inter-relationships.
It's one thing to 'know' the systems, it's another to actually understand it.
In their (sort of defence) you can't always blame the pilot for not having the depth of understanding of the 'machine'. The typical CASA engineering quiz that one does when doing a type endorsement is not detailed enough, in my opinion, and gaining access to aircraft engineering manuals &/or parts catalogues, is a difficult excercise and one has to actively seek out sympathetic engineers ormaintenance organisations in order to 'borrow' and copy pertinent parts of those manuals.
Personally, I always strived to get an engineers' type understanding of the machine and its parts - not that I could fix it airborne (or on the ground) - but that level of understanding allowed me to spot developing, or actual, problems and communicate those problems more effectively to the LAME's to give them a better chance at troubleshooting, fault finding & fixing the problem. That helped me maintain my schedule integrity, inform operations of foreseeable problems so they can re-plan things or get an effective rescue going early on in the piece - without comprimising safety.
When you know and understand the machine, you realise what a load of bollocks some of the pointlessly crazy stunts people pull with these aeroplanes.
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Jet_A_Knight aint dat de troof.
There are maybe thousands of young heroes out there who have never known how close to death by heavy blunt instrument they have come, when they tell the engineeer, whilst shrugging shoulders, "it's broken" and then are unable to accurately describe the sequence of events preceding the "breaking".
I've never met an engineer who wont help you out if you show you are genuinely interested in what he does.
To this day youngsters ask "how did you know that", simple really I just took the time to ask.
There are maybe thousands of young heroes out there who have never known how close to death by heavy blunt instrument they have come, when they tell the engineeer, whilst shrugging shoulders, "it's broken" and then are unable to accurately describe the sequence of events preceding the "breaking".
I've never met an engineer who wont help you out if you show you are genuinely interested in what he does.
To this day youngsters ask "how did you know that", simple really I just took the time to ask.
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I remember submitting additions for operations manual in order to get a PA31 added to the AOC. Our CASA foi would not accept it as it contained leaning instructions taken form the POH/faa approved flight manual, saying to lean the mixture to 25 degrees lean of peak when cruising. He insisted on making it 100 degrees rich of peak for cruise. It sappears that CASA believe they know more than the aircraft manufacturer, and the FAA.
So now the ops manual contains instructions that differ from the POH
Is this giving clear instructions to the pilots????? Which one are they supposed to follow?
What does this do for the credibility of the ops manual, or CASA?
How would this be viewed in a court of law>
Will pilots follow an ops manual which has data that contradicts the makers instructions?.
So now the ops manual contains instructions that differ from the POH
Is this giving clear instructions to the pilots????? Which one are they supposed to follow?
What does this do for the credibility of the ops manual, or CASA?
How would this be viewed in a court of law>
Will pilots follow an ops manual which has data that contradicts the makers instructions?.