Staying on the glideslope

[lowlycfi]

For the Double I's out there:What technique do you teach your instrument students to stay on the glideslope on an ILS? Pitch only, power only, or pitch and power together? Also, for those of you teaching instruments in the Cessna 172, what power settings, speeds and configuration(flaps) are you using during both precision and non-precision approaches? Just trying to hear different opinions.

 

[satpak77]

FlightSafety/Simuflite/"industry standards" dictate in turbine equipment you set a ball-park gouge power setting and worry about driving the airplane from GS intercept till runway in sight.

No jockeying throttles, etc etc. Remember, lets observe what we are doing. We are taking a flying airplane and steering down a path determined by a horizontal course and vertical course, under assumed 200/half IMC conditions. You need to be FLYING and LOOKING for the runway, not fly,look,check power, look, fly a little, give me some more throttle, ok good, fly, look, opps too much power, take some out, fly, look, etc etc

You will have to play with it. Your 1977 172 may require different setting that a 1998 C-172 with heavy avionics up front. Figure out your V-ref speed and round it up. If its 87, call it 90. Then remember the old rule of thumb with final approach speed and decent rate for 3 degree VASI or GS.

If vref = 90, then divide 90 by 2, this = 45, then put a zero on the end, that is 450. So at Vref, on a 3 degree slope, you should be (ballpark) showing a 450 FPM decent. Dont get too bent out of shape if its 400 or 500.

However, if its 1200, something aint right. This is a nice rule of thumb to enhance safety at those non-VASI airports at night.

Being a CFI, you obviously know the VSI lags. A side note, I tend to put the gear up immediately in a twin, however some disagree, and prefer to wait till "postive rate". My answer is, sh1t, I am flying right? By definition I am positive rate. However this is an old hangar discussion topic that will never die.

Play with the power settings that will give you this. In the turbine world, in almost all cases you are taught to be "configured for landing" at GS intercept, and you are concerned with FLY FLY FLY and LAND LAND LAND.

Also, observe the FAA's AC circular on stabilized approaches, part of being "stable" is in landing configuration at 1000 AGL if IMC or 500 FT AGL if VMC. I would argue this means power, flaps, gear, etc are set (AFM/POH is ultimate authority.)

my 2 cents

later

 

[nosehair]

Pitch to the Altitude - Power to the Airspeed

This is where it pays off. If you have learned to point, or pitch, your nose at a spot on the runway, and control your airspeed with power, then you will find pitching to the glideslope needle and following up with power for airspeed, if neccessary, to be a natural. If, however, you were trained to control airspeed with pitch, you will be all over the glideslope trying to keep the airspeed constant.
Of course, in the end, you will have to develop a smooth coordination of the two, but, until that day comes, pitch, (or fly) the nose up/down towards the glideslope needle. If you concentrate enough and respond quickly enough, the airspeed won't change by 10 knots, once you have the proper power setting. At first, just fly the glideslope needle, forget power/airspeed. After some practice with that, bring in slight power changes, if necessary, to keep the airspeed under control.
Start with about 2000 RPM / no flaps / 90kts in the 172. You will quickly find the prcise power setting, and if you like a little slower, and more configured for landing, try 80kts with 10 degrees flaps.
If you try to control glideslope with power, you're gonna be back-and-forth with the throttle. This is the reason I start out a brand-new student pitching to the altitude/glideslope and powering to the airspeed. Primacy.

 

[Snakum]

Dunno if this helps, but when first studying for the IR a few years ago my CFII had me determine the config for each phase of IR flight, and I was flying an N-model C172:

Cruise 115 kts - 2350 Clean
Cruise Descent - 2000 Clean Yellow Arc
Inbound FAF - 2200 Clean 90kts
Precision Descent (500 fpm) - 1950 Flaps 10 90kts
Non-precision Descent (900 fpm) - 1600 Flaps 10 90kts
MDA Cruise - 2250 Flaps 10 90kts

I developed my own checklists for each of the aircraft I flew using logical flows, etc. so I determined these config settings for each model and put it in the printed checklist, as well. I have all that stuff somewhere.

Minh

 

[FracCapt]

If, however, you were trained to control airspeed with pitch, you will be all over the glideslope trying to keep the airspeed constant.

Funny, I was trained - and have always trained students - to pitch for airspeed, power for altitude(in this case, to maintain the glideslope)....and I have no problem keeping the needles centered and airspeed on target. Very, very minor power changes - if any - are required if your airspeed starts to stray a little far.

What happens when you start getting up/downdrafts? Pitch up/down for the g/s, and just slam the throttle back and forth to maintain the airspeed? It's a lot less of a wild ride when you pitch for airspeed and use power to maintain the g/s....and it gives you much less of a chance to get behind the power curve. Not necessarily a problem in a 172 while flying an approach at 90kts....but when you're in a jet flying at VRef+10....losing a little airspeed can put you close to, or on, the back side of the power curve.

 

[satpak77]

also

I realize in light aircraft, such as C-172, with summer thermals and other stuff, this might not ALWAYS be the case, but

set power and fly the ILS and speed takes care of itself. Cover up airspeed and just drive down the slope, with your "ILS power setting" and you will be surprised how much yuo DONT need to stare at airspeed

remember V-ref is at 50 feet above touchdown, then you transition to touchdown speed, which in the C-172 should be stall plus some knots (dont have the exact figure but you get the idea. You are not touching down at 120 knots).

Also (and I will shut up) book POH landing distances assume you are at POH V-ref at the FAA 50 foot level, then transition to landing speed. Touchdown at v-ref (yes, guys do this) or anything out of POH specs, and you can throw the book landing distances out the window, since its unchartered territory.

 

[lowlycfi]

Thanks for the responses. I've had several instrument students over the last few months and the ballpark power setting and pitching using the vsi seems to work good.

 

[EDUC8-or]

Funny, I was trained - and have always trained students - to pitch for airspeed, power for altitude(in this case, to maintain the glideslope)....and I have no problem keeping the needles centered and airspeed on target. Very, very minor power changes - if any - are required if your airspeed starts to stray a little far.

What happens when you start getting up/downdrafts? Pitch up/down for the g/s, and just slam the throttle back and forth to maintain the airspeed? It's a lot less of a wild ride when you pitch for airspeed and use power to maintain the g/s....and it gives you much less of a chance to get behind the power curve. Not necessarily a problem in a 172 while flying an approach at 90kts....but when you're in a jet flying at VRef+10....losing a little airspeed can put you close to, or on, the back side of the power curve.

Yeah, what he said. Especially the part about up/downdrafts. I can't imagine keeping a constant power setting in a 172, encountering the typical FL summer thermals sometimes as high as GS intercept, and then pitching down to stay on my GS. If you don't reduce power (as suggested in a previous post) you're probably going to be overspeeding your 10 degree flap setting (typical IAP descent configuration) of 110. The last few days my students have really been reducing the power because it's getting hot. Without really touching the controls they are able to maintain the 90KT on gildeslope approach.

 

[midlifeflyer]

Wow! The makings of a pitch power debate that =doesn't= involve primary training.

Both methods work. It's all about energy management anyway, so it's about both pitch and power.

If you're riding high for example and you pitch for altitude without adjusting the power, your airspeed will increase. On the other hand, if you reduce power to recapture the glideslope and maintain the same pitch, your airspeed will decrease.

I think a lot of CFIIs teach pitching for the glideslope as the =initial= input because it's easier for a lot of people. The yoke generally reacts more immediately to pressure changes, our fingers on the yoke more sensitive to slight changes than on the throttle, and it's just a lot less work to make continuous slight changes in pressure on the yoke to maintain glideslope than to play with the throttle. And assuming we're not dealing with strong updrafts and downdrafts the airspeed variation will be so small that it's not worth worrying about.

In turbulence, since you have to do both anyway, it doesn't make a heck of a lot of difference which comes "first"

 

[standaman]

Pitch for airspeed and power for altitude is what I teach. I have seen students do it the other way as well. I honestly really don't care just as long as the students can meet standards. I will stay out of the pitch power debate.

 

[CaSyndrm]

WOW, I can't fathom all the technical jargin above. If you pull the nose up push the black handles forward. If you push the nose down pull the black handles backward. KISS method, chicks dig it. Formulas and memorization and other stuff can be dangerous in flight. It is always good to have a ballpark power setting for a plane your going to take a checkride in but other than that, DO WHATEVER IT TAKES to make it work. If the students are going to be professionals than multi-tasking with throttles and yokes shouldn't be a major challenge. One of the only major failures I ever witnessed in a simulator was a non precision approach with a pilot trying to figure out a mathmatical glide slope before and during the approach.

 

[EKUAVN20]

Pitch Changes

Funny this is posted...Just did one Yesterday at LEX...The best way I have been able to stay on the GS is have a constant power setting..In the 172R it was abt 1800 RPM... And use pitch changes, but also if you are using a timed approach more like a LOC approach or if partial panel you would have to keep a constant airspeed for the MAP... You dont want to be a Trombone player on the throttle that isnt very smooth...Just my 2 cents...