Hello,
Last time I flew in IMC, I did had a bit of struggle tracking the glide-slope when it was bumpy
On debrief, my instructor advised to try using elevator to track glide-slope and use power to adjust to approach speed, this makes ILS tracking easier in gusty conditions
I found this a bit confusing to what I used on my visual landings: speed = stick and power = slope
Do you have any thought how to get this wired correctly in my head?
The last thing I want is to get them confused in the heat of the moment 
In the military (and many civilian schools) we teach “point and power” for final approach control. I.e. you keep the aiming point in the correct position in the windscreen by pitch, and then use power adjustments to keep the desired approach speed. This is the same as the Instructor is recommending for the ILS where he means to use pitch corrections to adjust the descent rate and power to control airspeed. I have found over many years that this method for both produces students who can quickly control the final approach and go solo relatively quickly.
However….this is one of the most hackneyed debates of GA and many people will swear blind that “stick for speed and power for rate of descent” is the correct and only way to fly the final approach etc..
In reality the two are interconnected of course – I.e. pitch changes will induce a speed change and vice versa, proficient pilots instinctively adjust and control both to maintain the desired approach profile without thinking about it, but students need techniques to build that experience.
In truth, an adjustment to one control requires a corresponding adjustment to the other, so it’s a bit of a distinction without a difference but…
For IMC approaches, I was taught (and do) as your instructor said.
In VMC, I think both techniques are useful. Power = Speed for obstacle-free or alpine approaches (usually @ 1.3 Vso), and of course for hydroplaning approaches. Power = Slope for steeper, slower approaches in good weather, for instance over trees into a confined site or when trailing a rope – or just for fun.
Both approaches are correct as Jacko says they are interrelated. But I agree with your instructor. Point the plane where you want it to go and adjust power to set speed. On an ILS you are making small vertical position adjustments. Hard to do that with power IMHO. That said you should generally commence the ILS with an approximate power setting in mind.
That is what I had in mind nothing in stone, just pick his technique today for ILS tracking and stick with it during my training
Later as experience come in, I can combine all without thinking, as you mentioned both its all connected
It reminds me of landing super-cubs/motor-gliders, first you learn to land in open space with stick = speed target and power = slope target
When it gets tight, you start crossing the stick against power, side-slip and flaps/spoilers
JasonC wrote:
Hard to do that with power IMHO. That said you should generally commence the ILS with an approximate power setting in mind.
If I fly fixed(slope) then average(speed) and average(power) are linked, so yes I agree, I need to get an initial power setting in mind for the speed to fly before chasing the slope withe the stick
Ibra wrote:
Do you have any thought how to get this wired correctly in my head?
Yep! I reverse this for ILS approaches too. I treat it as though my yoke is hooked to the VSI. Aim for a RoD of the required fpm i.e. 500fpm.
Then you regulate speed with the throttle.
p.s. you can read the required fpm in published tables, depending on Groundspeed and glide slope in degrees. Put a straight edge along two to find the third.
you can read the required fpm in published tables
Multiply GS by 5 and you will be close enough for government work unless at Mannheim…
In quite a lot of aircraft you can actually set the power early in the approach and the aircraft naturally sorts itself out as you alter the configuration by flaps, gear etc, to a speed appropriate to where you are on the approach.
It is quite feasible to be descending in a Citation with a certain power setting and not touch the power levers again until you close the throttles to land. The speeds just work out as you put approach flap, drop the wheels at the glideslope, then landing flap at 3 or 4 miles. I think the magic number is about 55% in a CJ2+.
Point and power is the only way I’ve ever done instrument approaches
Thanks Archie for the table, it very handy for places where the gradient is not 5% (or 3 degrees slope)
It is even quicker to do approximate Aviator maths:
- 3 degrees, gradient = 3*3.14/1.8 give 5.2 so ROD = 5 * GS and height = 300*DME
- 4 degrees, gradient = 4*3.14/1.8 give 6.9 so ROD = 7 * GS and height = 400*DME
On average that should work, but my initial point was on how to do correction around the average when it is a bit convective/bumpy? as JasonC mentioned ILS is highly precise, so it will require sensitive stick inputs instead of power inputs as the effect of the letter is a bit slow. That said, when tracking slope with the stick it’s the average power that decides on your average speed as you highlight in the table
I will see how it goes next session, if it is calm then I just need to set power and relax no?
For the ILS, I fly with the yoke (or autopilot ) and use power to control the IAS.
For a nonprecision approach, I use the yoke (or the autopilot) to hold the rate of descent (say -500fpm) and use power to control the IAS. However Neil above is spot on and if you get the plane trimmed in level flight for say 90kt then dropping the gear and flap 1 will, on quite a lot of types AFAIK and certainly on the TB20, give you about -500fpm and still at 90kt.
Using power to control the rate of descent is an unstable way of doing it.
