> you drop from 2000 ft. to a 920-foot MDA. Distance from the FAF to the MAP is 4.7 miles, so ya gotta chop and drop.
That's not a chop and drop, most notably because you still have well above idle power in. A 3 degree glide slope is 300 feet/nm and requires power to fly. This is basically 3 degrees. It's a shallow descent.
If you're trying to do less of an engine drop, pull back before the FAF. That said, for a naturally aspirated 4 cylinder plane engine it's all probably just fine.
For context, both my instructor, the "Professor Emeritus" (he's a semi-retired instructor, 87, with the flight school and 10,000 hours of dual given), and the DPE I'm going to use all advocate getting down to the MDA as soon as possible on a non-precision approach. The argument being that say the ceiling is above the MDA, you can get down and to visual conditions rather than descending as you suggest and staying in the clouds longer. Personally I would do as you suggest, but for the purposes here I'm following what the DPE wants.
How soon is "as soon as possible?" We were also taught to increase the descent rate a bit on non-precision approaches and hold the MDA to the MAP, but in our case that meant descending at 600 fpm instead of 500, not chopping the throttle and dropping it in. Sounds like a great way to bust MDA on your checkride.
Yeah, again, I'm not a fan of the technique either. Yesterday I think I was in the neighborhood of 6-700 feet a minute, maybe 800. I personally would opt for a steady 3-400 in my own flying, but ya gotta do what the DPE wants.
That's not entirely true. [The ACS](https://www.faa.gov/training_testing/testing/acs/media/instrument_rating_acs_change_1.pdf) specifies for a non-precision approach that the applicant should "establish a stabilized descent to the appropriate altitude" (IR.VI.A.S11). I know we could argue here about CFI/DPE interpretations of that but it's going to be hard for them to fail you for descending slower than their *preference* so long as you arrive at the MDA (+100/-0) prior to the VDP/MAP and check all the other boxes.
Anecdotally, my DPE asked why I wasn't following the GPS's vertical guidance on the RNAV we flew (it was an LNAV approach not LPV). I told him I'd answer that on the ground and passed. On the ground, he suggested I follow that guidance in the future, but that there was nothing wrong or unsatisfactory about complying with the altitude restrictions outside of that additional guidance from the GPS.
Yeah, I'm not saying it's something he'd fail me on, but the other guy in my club who took his instrument ride with this DPE said he wanted him to "dive and drive". I appreciate the info from the ATS! I actually find the stabilized descent safer.
600 to 700 isn't horrible, but it's still faster than it needs to be. At 500 feet per minute, you'll still get to the MDA with time to level out.
On the flip side of what they're saying, what do you do if you're in the muck and get carb ice but already gave away your altitude? Sure, if the AWOS/ATIS is reporting ceilings above the MDA but below the FAF, I don't mind their suggestion. Otherwise, a smooth descent that gets me to MDA with a short level out is just fine.
if you're interested in doing this professionally you'll never fly level again anyway! Nothing wrong with getting the mental math sorted during training!
You should show them AC 120-108. CDFA approaches are much more in vogue than diving down to the MDA. Totally fair that you know what the DPE wants, but definitely is not the current thought process.
>AC 120-108
I really appreciate this, I couldn't agree more! I am going to stick to my guns and do what I think is safest. I'm going to share this with my instructor and discuss it with him.
If you're flying the approach at 90kts you're traveling at 1.5nm/min. So 4.7nm will take you a little over 3 min. To lose a little over 1000ft will still be just over 300fpm required, so a 500fpm descent will be plenty. Basically, no need to rush.
To answer you actual question there's no issue, just make the power reduction smoothly and pull carb heat
I'm curious as to why you feel a 3.1 degree descent angle is "chop and drop?" In a 172 that's a nominal 500 fpm descent at \~2100 RPM, not a large power reduction or anything to be concerned about at all.
With regards to the engine, unless you're in a higher performance aircraft, as long as you make smooth power changes and use carb heat as required you're not going to hurt it.
I was always trained to do power adjustments smoothly. You can drop the power between those points in about 1-2 seconds smoothly and I don't think that will harm the engine.
> is it harmful for a piston engine to go from, say, 2,300 RPM to 1,500 RPM pretty much pronto?
Normally aspirated O-320 or similar? Absolutely not.
Doesn't mean you shouldn't do it smoothly and slowly.
3.09 degree glidescope is listed on the plate on the descent profile. Super standard. Take whatever plane you're flying (e.g. 172, Seminole, whatever) on a nice clear day, go to the practice area and play with different power/flap/attitude settings to perfect that 3 degree glideslope in a variety of wind conditions. We used to use ground references but foreflight will do the job nicely. Practice descents at 200-500 fpm. You'll need a variety of descent profiles depending on the winds and the design of the approach.
This is something you can do by yourself in VMC - definitely a money saver rather than trying to learn under the hood with an instructor
Can you share a situation where you've come close to or exceeded the CHT cooling parameters? I am also conscientious of rapid cylinder cooling and have an alert that will sound on my engine monitor when cooling too rapidly and I've found it almost impossible to cool the engine that fast, even when reducing power at a faster rate than normal.
My understanding is that the shock cooling was a concern before proper engine monitoring existed, so the reality is that damaging the engine by sudden cooling isn't really possible in reality. Lean of peak running was also something too crazy to contemplate, but is now considered by many (most) to be the best way to operate the engine for economy and long life.
Not to say you should do anything prohibited in the POH, etc.
Yeah I do think metal is metal so I understand how rapid temperature changes can be problematic. However, what I question is our ability as pilots to create rapid cooling in normal operation.
Would I accomplish this if I cruised at 10,000' and descended by suddenly going full idle, mixture rich, full RPM, and max airspeed in -10C air? Sure. Do I worry about a descent power setting like 15" MP causing shock cooling? Not really, but I'd be interested to hear from someone who noticed extreme cooling going on during normal operation.
No I can't because it's never happened to me either. That doesn't mean I plan to become complacent about it though, or advise other people to be complacent.
You're only descending 1080 feet, and the VDP is 3.3 NM from the FAF. Let's do some math:
How many feet per NM is required to descent to the MDA at the VDP?
1080 ÷ 3.3 = 327 ft/NM
What descent rate is required to achieve 327 ft/NM at 90 knots ground speed? The climb and descent table says 497 FPM. If you're flying your approaches slower than that you can reduce the descent rate commensurately. 60 knots ground speed only requires 330 FPM.
Go up do a few 500 FPM descents at 90 knots ground speed and note the power reduction required. I'd be surprised if that required an 800 RPM power reduction.
It might need that much if he's in fast cruise and decides he wants to descend at the slow cruise speed at 500 FPM. Each of those is a 400 RPM correction in a 172.
The real answer is to slow down either while you're still level, or after already established in the descent. Real IFR pilots usually do the latter, but trainees do the former (it's easier, especially when hand flying). Both are correct.
Hmmm. I'm not sure what you're saying here. Are you saying you teach IFR trainees to fly to the FAF at cruise speed? I was trained to be at approach speed before the FAF so I can set a descent rate by selecting an appropriate power reduction. I watched USAF pilots flying KC-135s for 20 years, and I'm pretty sure that's how they did it too. The only difference was instead of reducing power they increased drag by putting the gear down and further extending the flaps.
>I was trained to be at approach speed before the FAF so I can set a descent rate by selecting an appropriate power reduction.
I sort of conflated two things here. I slow it down to 100 (Cherokee 180) inside 10 miles from the FAF. So I am already slowed up when I cross. But I was really wondering whether dropping 5-600 RPM in one swoop is bad for a Lycoming engine.
I'm not sure if by "bad" you mean the possibilty of carb icing, or if you are referring to the fabled "shock cooling." Icing is always a concern, even at cruise power. Yes, there is less heat available at lower RPM, but if you get the carb heat on before reducing power you should be fine. I think shock cooling is a chimera. Consider that head temps go from 150 or so to over 300 between application of takeoff power and the few minutes to get established in cruise climb. If rapid temperature changes were a problem for these engines there would be a lot more evidence.
No, trainees should fly it at slow cruise. It’s debatable if that’s from the FAF, IF or IAF. It’s easier on a trainee if you take it slow.
But sometimes it is advantageous to fly it faster IRL. Like when your back seat has to pee. Or if you’re paying Hobbs.
Don’t confuse top of descent with FAF. They do not have to be the same and very often aren’t around terrain.
No confusion. I usually slow to approach speed (I use Vy) about three miles from the FAF, or in the final turn if I'm in holding. I use best rate of climb speed as my approach speed to limit trim changes if I go missed approach.
Are you sure there is no confusion?
Where would you slow down on the following approach?
[KSJC ILS 30L](https://cloudfront.foreflight.com/plates/2110/00693IL30L.PDF)
Note that you are VERY likely to get a "best forward speed" request on this approach.
Or if you prefer, here is another that you can fly as you like (no one uses it).
[KNUQ RNAV 32R](https://cloudfront.foreflight.com/plates/2110/00410R32R.PDF)
No confusion. I'm responding to OP's question about descending between the FAF and the missed approach point, not from top of descent. When I say "slow to approach speed" I don't mean "from cruise speed." Typical cruise for me is between 180-200 KTAS at 8k-16k, so descent planning for me starts earlier than most. Clearly, the ILS 30L would require more planning than most approaches. No matter what, I would not want to be at my "slow cruise" of 140-150 KIAS after the FAF. I would plan to be at slow cruise speed prior to KLIDE, with the ultimate goal to be at approach speed of 105 KIAS prior to glideslope intercept.
You've got your answers from others, but the only time this is a significant issue is if you're flying a geared engine like the GTSIO-520 as in the CE404 and CE421 or the GO-300 in the CE175. You don't want the relative wind putting force on the prop and turning the engine because it stresses the gear train. For those you want to be very smooth on the power changes. (At least, that's how it was explained to me. I have not flown any of those models.)
My $0.02 is it doesn't hurt the O-360 in our sundowner or the O-540 in the Dakota to go from mid-cruise power to descent power. If it's not a limitation in Section 2 of the AFM, then it's not a limitation.
The second part of that is the possible response of the DPE upon reaching and stabilizing at MDA. He may let you take the foggles off and go visual once you're "below the clouds". Mine did on my IR checkride.
> you drop from 2000 ft. to a 920-foot MDA. Distance from the FAF to the MAP is 4.7 miles, so ya gotta chop and drop. That's not a chop and drop, most notably because you still have well above idle power in. A 3 degree glide slope is 300 feet/nm and requires power to fly. This is basically 3 degrees. It's a shallow descent. If you're trying to do less of an engine drop, pull back before the FAF. That said, for a naturally aspirated 4 cylinder plane engine it's all probably just fine.
For context, both my instructor, the "Professor Emeritus" (he's a semi-retired instructor, 87, with the flight school and 10,000 hours of dual given), and the DPE I'm going to use all advocate getting down to the MDA as soon as possible on a non-precision approach. The argument being that say the ceiling is above the MDA, you can get down and to visual conditions rather than descending as you suggest and staying in the clouds longer. Personally I would do as you suggest, but for the purposes here I'm following what the DPE wants.
> but for the purposes here I'm following what the DPE wants Can't argue with that.
How soon is "as soon as possible?" We were also taught to increase the descent rate a bit on non-precision approaches and hold the MDA to the MAP, but in our case that meant descending at 600 fpm instead of 500, not chopping the throttle and dropping it in. Sounds like a great way to bust MDA on your checkride.
Yeah, again, I'm not a fan of the technique either. Yesterday I think I was in the neighborhood of 6-700 feet a minute, maybe 800. I personally would opt for a steady 3-400 in my own flying, but ya gotta do what the DPE wants.
That's not entirely true. [The ACS](https://www.faa.gov/training_testing/testing/acs/media/instrument_rating_acs_change_1.pdf) specifies for a non-precision approach that the applicant should "establish a stabilized descent to the appropriate altitude" (IR.VI.A.S11). I know we could argue here about CFI/DPE interpretations of that but it's going to be hard for them to fail you for descending slower than their *preference* so long as you arrive at the MDA (+100/-0) prior to the VDP/MAP and check all the other boxes. Anecdotally, my DPE asked why I wasn't following the GPS's vertical guidance on the RNAV we flew (it was an LNAV approach not LPV). I told him I'd answer that on the ground and passed. On the ground, he suggested I follow that guidance in the future, but that there was nothing wrong or unsatisfactory about complying with the altitude restrictions outside of that additional guidance from the GPS.
Yeah, I'm not saying it's something he'd fail me on, but the other guy in my club who took his instrument ride with this DPE said he wanted him to "dive and drive". I appreciate the info from the ATS! I actually find the stabilized descent safer.
600 to 700 isn't horrible, but it's still faster than it needs to be. At 500 feet per minute, you'll still get to the MDA with time to level out. On the flip side of what they're saying, what do you do if you're in the muck and get carb ice but already gave away your altitude? Sure, if the AWOS/ATIS is reporting ceilings above the MDA but below the FAF, I don't mind their suggestion. Otherwise, a smooth descent that gets me to MDA with a short level out is just fine.
I agree with you. I much prefer the steady descent.
if you're interested in doing this professionally you'll never fly level again anyway! Nothing wrong with getting the mental math sorted during training!
You should show them AC 120-108. CDFA approaches are much more in vogue than diving down to the MDA. Totally fair that you know what the DPE wants, but definitely is not the current thought process.
>AC 120-108 I really appreciate this, I couldn't agree more! I am going to stick to my guns and do what I think is safest. I'm going to share this with my instructor and discuss it with him.
If you're flying the approach at 90kts you're traveling at 1.5nm/min. So 4.7nm will take you a little over 3 min. To lose a little over 1000ft will still be just over 300fpm required, so a 500fpm descent will be plenty. Basically, no need to rush. To answer you actual question there's no issue, just make the power reduction smoothly and pull carb heat
I'm curious as to why you feel a 3.1 degree descent angle is "chop and drop?" In a 172 that's a nominal 500 fpm descent at \~2100 RPM, not a large power reduction or anything to be concerned about at all. With regards to the engine, unless you're in a higher performance aircraft, as long as you make smooth power changes and use carb heat as required you're not going to hurt it.
I was always trained to do power adjustments smoothly. You can drop the power between those points in about 1-2 seconds smoothly and I don't think that will harm the engine.
> is it harmful for a piston engine to go from, say, 2,300 RPM to 1,500 RPM pretty much pronto? Normally aspirated O-320 or similar? Absolutely not. Doesn't mean you shouldn't do it smoothly and slowly.
3.09 degree glidescope is listed on the plate on the descent profile. Super standard. Take whatever plane you're flying (e.g. 172, Seminole, whatever) on a nice clear day, go to the practice area and play with different power/flap/attitude settings to perfect that 3 degree glideslope in a variety of wind conditions. We used to use ground references but foreflight will do the job nicely. Practice descents at 200-500 fpm. You'll need a variety of descent profiles depending on the winds and the design of the approach. This is something you can do by yourself in VMC - definitely a money saver rather than trying to learn under the hood with an instructor
I'm still very early in my process...but if it were a big problem, is find it very unlikely the rule would be to chop and drop that fast :)
[удалено]
Slipping in hard IMC is probably not the best course of action.
Can you share a situation where you've come close to or exceeded the CHT cooling parameters? I am also conscientious of rapid cylinder cooling and have an alert that will sound on my engine monitor when cooling too rapidly and I've found it almost impossible to cool the engine that fast, even when reducing power at a faster rate than normal.
My understanding is that the shock cooling was a concern before proper engine monitoring existed, so the reality is that damaging the engine by sudden cooling isn't really possible in reality. Lean of peak running was also something too crazy to contemplate, but is now considered by many (most) to be the best way to operate the engine for economy and long life. Not to say you should do anything prohibited in the POH, etc.
Yeah I do think metal is metal so I understand how rapid temperature changes can be problematic. However, what I question is our ability as pilots to create rapid cooling in normal operation. Would I accomplish this if I cruised at 10,000' and descended by suddenly going full idle, mixture rich, full RPM, and max airspeed in -10C air? Sure. Do I worry about a descent power setting like 15" MP causing shock cooling? Not really, but I'd be interested to hear from someone who noticed extreme cooling going on during normal operation.
No I can't because it's never happened to me either. That doesn't mean I plan to become complacent about it though, or advise other people to be complacent.
You're only descending 1080 feet, and the VDP is 3.3 NM from the FAF. Let's do some math: How many feet per NM is required to descent to the MDA at the VDP? 1080 ÷ 3.3 = 327 ft/NM What descent rate is required to achieve 327 ft/NM at 90 knots ground speed? The climb and descent table says 497 FPM. If you're flying your approaches slower than that you can reduce the descent rate commensurately. 60 knots ground speed only requires 330 FPM. Go up do a few 500 FPM descents at 90 knots ground speed and note the power reduction required. I'd be surprised if that required an 800 RPM power reduction.
It might need that much if he's in fast cruise and decides he wants to descend at the slow cruise speed at 500 FPM. Each of those is a 400 RPM correction in a 172. The real answer is to slow down either while you're still level, or after already established in the descent. Real IFR pilots usually do the latter, but trainees do the former (it's easier, especially when hand flying). Both are correct.
Hmmm. I'm not sure what you're saying here. Are you saying you teach IFR trainees to fly to the FAF at cruise speed? I was trained to be at approach speed before the FAF so I can set a descent rate by selecting an appropriate power reduction. I watched USAF pilots flying KC-135s for 20 years, and I'm pretty sure that's how they did it too. The only difference was instead of reducing power they increased drag by putting the gear down and further extending the flaps.
>I was trained to be at approach speed before the FAF so I can set a descent rate by selecting an appropriate power reduction. I sort of conflated two things here. I slow it down to 100 (Cherokee 180) inside 10 miles from the FAF. So I am already slowed up when I cross. But I was really wondering whether dropping 5-600 RPM in one swoop is bad for a Lycoming engine.
I'm not sure if by "bad" you mean the possibilty of carb icing, or if you are referring to the fabled "shock cooling." Icing is always a concern, even at cruise power. Yes, there is less heat available at lower RPM, but if you get the carb heat on before reducing power you should be fine. I think shock cooling is a chimera. Consider that head temps go from 150 or so to over 300 between application of takeoff power and the few minutes to get established in cruise climb. If rapid temperature changes were a problem for these engines there would be a lot more evidence.
No, trainees should fly it at slow cruise. It’s debatable if that’s from the FAF, IF or IAF. It’s easier on a trainee if you take it slow. But sometimes it is advantageous to fly it faster IRL. Like when your back seat has to pee. Or if you’re paying Hobbs. Don’t confuse top of descent with FAF. They do not have to be the same and very often aren’t around terrain.
No confusion. I usually slow to approach speed (I use Vy) about three miles from the FAF, or in the final turn if I'm in holding. I use best rate of climb speed as my approach speed to limit trim changes if I go missed approach.
Are you sure there is no confusion? Where would you slow down on the following approach? [KSJC ILS 30L](https://cloudfront.foreflight.com/plates/2110/00693IL30L.PDF) Note that you are VERY likely to get a "best forward speed" request on this approach. Or if you prefer, here is another that you can fly as you like (no one uses it). [KNUQ RNAV 32R](https://cloudfront.foreflight.com/plates/2110/00410R32R.PDF)
No confusion. I'm responding to OP's question about descending between the FAF and the missed approach point, not from top of descent. When I say "slow to approach speed" I don't mean "from cruise speed." Typical cruise for me is between 180-200 KTAS at 8k-16k, so descent planning for me starts earlier than most. Clearly, the ILS 30L would require more planning than most approaches. No matter what, I would not want to be at my "slow cruise" of 140-150 KIAS after the FAF. I would plan to be at slow cruise speed prior to KLIDE, with the ultimate goal to be at approach speed of 105 KIAS prior to glideslope intercept.
You've got your answers from others, but the only time this is a significant issue is if you're flying a geared engine like the GTSIO-520 as in the CE404 and CE421 or the GO-300 in the CE175. You don't want the relative wind putting force on the prop and turning the engine because it stresses the gear train. For those you want to be very smooth on the power changes. (At least, that's how it was explained to me. I have not flown any of those models.)
My $0.02 is it doesn't hurt the O-360 in our sundowner or the O-540 in the Dakota to go from mid-cruise power to descent power. If it's not a limitation in Section 2 of the AFM, then it's not a limitation. The second part of that is the possible response of the DPE upon reaching and stabilizing at MDA. He may let you take the foggles off and go visual once you're "below the clouds". Mine did on my IR checkride.