TD,
Those are great wives tales, but tell me, how many engine failures have you had to get those stats? How many of them shook out the way you described? How many cylinders have you changed as a result of shock cooling?
On the east coast most airplanes might make an airport during an engine failure at cruise. Elsewhere...the odds aren't great.
What has TBO to do with the price of tea in china? Shock cooling doesn't affect TBO. Tea doesn't affect TBO. Nothing affects TBO. It's an arbitrary imaginary reference number assigned by the manufacturer for first-run engines.
However, shock cooling can drasticaly shorten the life of an engine. It's an age old debate, but generally those who are on the side of the fence that says it doesn't happen, have never been around to see it happen. I have, and I can assure you, it does.
172, I'm sorry you find my reply condescending. I stated nothing but facts. These are basic facts, and should come as no surprise, nor were they intended to be condescending. I know nothing of your experience, nor do I presume to know you or your expeience. I addressed only the words that were applied in the initial post of the thread.
I understand the common desire to reach the runway if something happens. However, I've spent a great deal of my flying career at low level (below powerlines, most of it), and there has been zero chance of reaching any kind of landing surface during most of that time. I find it humerous and incongruous, then, when it suddenly becomes so important to make the runway in the pattern. It isn't.
Most engine failures do not occur duing power changes. They occur arbitrarily. In some cases the failures are enhanced or manifest by the change; most failures are partial failures involving a component or system and not complete or catastrauphic failures. In many cases, such a failure may be undetected at a current setting but may be manifest at a higher setting, etc. I have seen this happen on a number of occasions.
Some of my most spectacular cylinder failures have been far from a runway and during constant power in cruise. Others have been during takeoff. I don't recall ever having one outside training during landing (with the exception of several successive failures during rollout in a C-130 due to a progressive leak onto the 5th and 10th bleeds), and on only two occasions have I had failures during a go-around (both in single engine airplanes). Looking back on various types of failures, I can't see any pattern that suggests they occured primarily during power changes, near airports, or any other consistent criteria.
If you do lose your only engine, you won't necessarily be doing a power off landing. You may very well be doing a partial power landing. I have had a number of these, because the most common type of engine failure is a partial failure. This may be a cylinder loss, carb or injection failure, induction leak, slipped mag or bad mag, or any number of other possible situations.
Certainly one should be familiar and conversant with emergency proceedures, as I detailed in my last post. However, as a matter of course, teaching regular landings without power in piston airplanes is bad form, and poor technique.
A 3 degree glideslope or approach angle is a standard glideslope, and is not a low angle at which to approach the runway.
There are other factors involved that make a power off approach unsatisfactory. Among them is backlash issues; something that's normally not a consideration for automotive engines. In aircraft engines, however, you should strive to never allow the propeller to drive the engine, if possible. All internal clearances, and even the mag settings, are predicated upon established backlash for proper spacing and timing. Stresses are typically incured in one direction. Excessive power off running of the engine, at manifold pressures insufficient for the engine to drive the prop, leave the prop to drive the engine and this reduces engine life. It also increases stresses and reverses loadings on critical components such as connecting rods.
A power off approach cools the engine, and reduces the level of carburetor heat available if needed. Most instructors seem to believe that the most likely time for carb ice to form is a power off descent. However, this isn't true. The most likely time for it to form is during the initial power up, following a power off descent. I've seen engine failures occur that can be directly attributed to this under the right circumstances. In such cases, often insufficient heat was available on short notice, due to an extended power off descent.
Many engines used for light training airplanes are reasonably tolerant of abusive power changes such as rapid throttle movement and power off descents. However, simply because one can get away with such abuse in these engines, does not make it acceptable in most piston aircraft engines. In many engines, it can lead to a rapid demise of the engine. Always treat the engine like your life depends on it, because it does.
Good habits in training airplanes translate to aircraft that are not training airplanes. Power off descents in turbocharged or geared engines, or in large bore engines and counterweighted crankshafts are to be avoided. Many airplanes shouldn't be brought below the bottom of the green arc on manifold pressure during the approach, and RPM and temperature must sometimes be carefully monitored. The time to instill these proper habits is during primary training, when the pilot should be taught to use proper power management and proper engine care.
I realized I had a lot to learn about engines as a student when I applied power in a J-3 to go around for some deer on the runway. The engine quit, and I quickly learned to baby the throttle. You can get away with rapid power application in an 0-235, but not in an A-65 or C-85. You shouldn't perform rapid power application, but many engines in use in light aircraft today, especially training aircraft, permit bad habits without much complaint. That doesn't make it right.
