Winds on approach

"paul kgyy" wrote in message
ps.com...
Consistency is valuable when you're still getting the hang of IFR
approaches. However, once past the initial phase, you need to
practice approaches at different speeds because eventually you will
need to move the airplane along with traffic behind you. Also, I find
that in windy conditions, a faster approach is easier to control so
often add an inch of MP to my customary power setting.

When it's gusty, yes - you'd always add a squirt of power above the normal
approach speed just to cater for Sod's law which states that you'll get a
lull half a second before you flare, and the concrete will happen rather
more noticeably than you hoped.

I'd attach a caveat concerning the aircraft behind you, though. Yes, it's
good to be nice to him/her if it's convenient and safe to do so, but
remember that (a) you're primarily responsibility for the safety of your
aircraft, not the convenience of his/hers; and (b) the manufacturer of your
aircraft wrote the POH, not the ATC guy or the bloke behind you :-)

D.

You should fly your normal approach *indicated airspeed*, not ground
speed.

This is particularly important if it's windy and bumpy. If you fly
that approach at cruise power to keep the groundspeed at 90 knots
you're likely above your Va, which can overstress the airframe.

On Mar 29, 12:59 pm, "kevmor" wrote:
I flew yesterday and did some practice approaches, and the winds were
about 20 knots gusting to 26-28. I've flown almost all approaches so
far in a different 172 that had a 180hp conversion. Because of the
winds, I kept almost full cruising power on the descents to try and
maintain my normal 90 kts ground speed for timing and roughly 500fpm
for the ILS.

This plane did have an IFR GPS indicating ground speed, but the one
I've been using for all other approaches didn't, neither DME. The CFI
informed me I should have used known power settings. What are your
thoughts? I'm not sure how I would've known the right power setting,
unless I used what I normally do, and accept the lower ground speed,
then adjust my descent for the ILS to a much lower fpm descent?

"M" wrote in message oups.com...


This is particularly important if it's windy and bumpy. If you fly
that approach at cruise power to keep the groundspeed at 90 knots
you're likely above your Va, which can overstress the airframe.

A touch of hyperbole, maybe?
Va is the G-safe speed for *abrupt full deflection* of any control.
Most of my ILS approaches thankfully don't require that. :-)

On Mar 30, 8:42 am, "John R. Copeland"
wrote:
"M" wrote in ooglegroups.com...

This is particularly important if it's windy and bumpy. If you fly
that approach at cruise power to keep the groundspeed at 90 knots
you're likely above your Va, which can overstress the airframe.

A touch of hyperbole, maybe?
Va is the G-safe speed for *abrupt full deflection* of any control.
Most of my ILS approaches thankfully don't require that. :-)

A big gust of wind with vertical components can put a lot of stress on
airframe. Va doesn't completely protect you against bent airframe
in turbulence but it provides a lot more protection than a typical
criuse IAS.

"kevmor" wrote in message
ups.com...
I'm not sure how I would've known the right power setting,
unless I used what I normally do, and accept the lower ground speed,
then adjust my descent for the ILS to a much lower fpm descent?

That's what I'd do. The key is that you're doing the things you do in the
right places, not at any specific speed. So as long as the places and
altitudes that you turn and/or descend correspond to what it says on the
approach plate, that's just peachy - it'll stop you banging into mountains
and whatnot. Yes, you'll end up with a lower rate of descent in order to
keep the glideslope needle centred, but that's perfectly normal.
Additionally, the POH says that you should approach at such-and-such a
speed, so do so - the wing doesn't care how fast the sky is moving over the
ground, only how fast it's moving over the aerofoil.

If you want to keep the power up for a bit longer than normal just so you
don't grow old waiting for the glideslope to come down to meet you, then
that's up to you. But by the time you're established on your approach, you
ought to be at your proper approach airspeed - once established it's a
non-trivial task to adjust your speed markedly, then fix the rate of descent
to compensate for all that thrust you just took off, all the while ensuring
you're still on the glideslope.

Assuming you're into a headwind, the groundspeed is largely irrelevant -
except that you'll wear the tyres out a little bit less than usual, and
you'll have further to taxi once you've landed, as the landing roll will be
shorter than usual.

D.

On 29 Mar 2007 12:59:55 -0700, "kevmor" wrote:

There have been a lot of answerers to this and I've not read the who
thread. but there are some very important things to take into account.
I flew yesterday and did some practice approaches, and the winds were
about 20 knots gusting to 26-28. I've flown almost all approaches so
far in a different 172 that had a 180hp conversion. Because of the
winds, I kept almost full cruising power on the descents to try and
maintain my normal 90 kts ground speed for timing and roughly 500fpm
for the ILS.

You are flying an airplane, you are not driving a car. You fly the
proper airspeed! If an ILS you adjust the power to maintain the GS.
Remember you fly the airplane, CALCULATE the ground speed
and from that derive the time. Your time will change with the winds.

Think of it this way. If you had a 30 knot tail wind would you slow up
by 30 knots from your regular approach speed? More than likely that
would put your below stall speed.

This plane did have an IFR GPS indicating ground speed, but the one
I've been using for all other approaches didn't, neither DME. The CFI
informed me I should have used known power settings. What are your

Yup! IOW you need to maintain the proper airspeed and rate of descent
where necessary.

thoughts? I'm not sure how I would've known the right power setting,

You will eventually learn to set the power to get the speed or rate of
descent at the speed you want. Although the power settings between the
two planes may be different there is going to be little difference in
the approach speeds.

unless I used what I normally do, and accept the lower ground speed,

Yes

then adjust my descent for the ILS to a much lower fpm descent?

Yes

As I said, you are flying an airplane in the air, not driving a car on
the ground. You fly the airplane at the proper speed and take what
ever ground speed you get. From that you calculate or derive your
times. You should try flying an ILS in a high performance plane with
a 30 knot tail wind, followed by a circle to land:-)) I normally
fly approaches at 120 be they step down or precision. I land VFR at 80
MPH minus 1 MPH for each 100 # under gross. That means I have a lot
of slowing up to do. Now add a 30 knot tail wind and I'm coming down
the ILS with 150 for ground speed. I have to circle at low altitude
and lose 70 MPH in the process. Actually that is for the over the
fence speed so I will need to lose about 80 to 90 MPH before I can get
the wheels on the runway.

BTW I rarely look at the power settings coming down the ILS. When I
adjust the power (MP in this case) to stabilize at 120. When I
intercept the GS I drop the gear while holding a level attitude. This
alone should put me right on the GS at the proper rate of descent. I
do know that 1" +/- MP will change the rate of descent 100 FPM. I do
look at the MP gage to get the one inch, but I really don't pay much
attention to the actual reading. Nor do I look out the window at the
scenery for visual clues as to GS as I don't care what the ground
speed turns out to be. I'm only concerned about air speed.
Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com