Approach speeds for ILS

"Richard Kaplan" wrote
I would say an overrun cannot happen in a 172 on ILS into the wind or with
calm winds as long as the power is cut at decision height. If the airspeed
is high as discussed in this thread and the airplane is on the glideslope,
then the airplane should be within gliding distance of the runway at
decision height.

Yes, that's true. However, I consider an immediate power cut at
decision height to be poor procedure. The normal ILS is flown on a 3
degree glideslope. However, the power-off glide in anything
approaching landing configuration (meaning gear down if retractable
and at least some flaps) will be 7-10 degrees. So a power cut at DH
means a significant pitch change at low altitude. Since most of the
fleet has tractor props and conventional tails, the power cut will
also cause a significant out of trim condition - nose down. In good
vis and with a Skyhawk-class airplane, it's not a big problem. Try
that trick in your C-210 or my PA-30 in less than a mile vis, and
unless you've practiced it extensively and recently, the landing is
goint to be very, very ugly - possibly ugly enough for maintenance
bills. People have been known to drive the gear right through the
wings doing this.

Since my IFR students are either flying high performance singles or
twins or expect to move into them, I just can't see teaching the
procedure you seem to be advocating. I instead teach a gradual power
reduction with retrim, such that the pitch attitude never really
changes and the airspeed bleeds off gradually. Yes, it eats more
runway and on short runway may require a speed reduction on the ILS,
but it seems like a beter tradeoff. Personally, I slow to about
95-100 mph (not kts) on the ILS at about 300 ft, which seems like the
best compromise between retaining the option for a single engine
missed approach and allowing a landing with a tailwind on a short ILS
runway. In a single engine plane, I see no reason not to slow down
further out. I know that an ILS can be flown in a Bonanza at 90 mph
in turbulence - I've seen an instrument student do it.

As far as flying an ILS with a tailwind, I agree that could cause an
overrun. I would also suggest that landing out of an ILS in actual IMC
conditions with a tailwind is an exercise which should be attempted only by
an experienced, advanced IFR pilot and/or with an experienced CFII on-board.

Well, I like to give my student the necessary tools to handle it. Of
course since I don't instruct renters and don't deal with FBO's,
finishing in the minimum allowable 40 hours is not my highest priority
- nor theirs.

In particular, a pilot who is uncomfortable flying a high-airspeed ILS with
a headwind certainly should not attempt a tailwind ILS.

Now that I can agree with. A high speed ILS is certainly something I
consider important. It's just that a high speed ILS and a tailwind
landing on a short runway simply don't mix.

Michael

"Richard Kaplan" wrote in message ws.com...
ILS runways are usually 5,000 feet or longer. You could dissipate speed
over the runway.

I suspect if you cross the runway threshold right on the glideslope at 90
knots in a Skyhawk with a 5,000 foot runway, there is no way you could
overrun the runway if you tried.

I don't know about a Skyhawk, but FWIW, our former home airport
used to have only 1 ILS, to Rwy 8 which meant if low wx combined with
wind, one might be landing with a tailwind (prevailing winds from
west in these parts). As a training exercise, one time I kept my
speed up to 90 kts over the threshold. I didn't run off the runway,
but I was durn close to my "go around!" point before my plane
decided to quit flying and settle down. I definately landed on
the last 3rd of a 6,500 ft runway. Dunno what the tailwind was --
nothing too startling (10-12 kts?)

Unfortunately, since many training ILS are done to a missed
approach, landing from an ILS isn't something at which some
instrument pilots get a lot of practice.

Cheers,
Sydney

"Snowbird" wrote in message
om...

the last 3rd of a 6,500 ft runway. Dunno what the tailwind was --
nothing too startling (10-12 kts?)


That is a very significant tailwind for landing; it would not surprise me if
a 10 knot tailwind doubled your landing roll vs. a 10 knot headwind or if
the total landing distance increased between 50% and 100%.


--
Richard Kaplan, CFII

www.flyimc.com

"Richard Kaplan" wrote in message ws.com...
"Snowbird" wrote in message
om...
the last 3rd of a 6,500 ft runway. Dunno what the tailwind was --
nothing too startling (10-12 kts?)

That is a very significant tailwind for landing; it would not surprise me if
a 10 knot tailwind doubled your landing roll vs. a 10 knot headwind or if
the total landing distance increased between 50% and 100%.

Hi Richard,

As far as I could tell, it didn't do a thing to my landing roll.
What it affected, drastically, was the distance it took my plane
to slow to landing speed and consent to stop flying.

I'm very glad I had a CFI who had me try this. Experience is
worth 1000 words. After doing so, I can easily see how an overrun
accident (or loss of control if someone tried to force the plane to
land) could occur on a long, ILS-served runway.

One size definately does not fit all situations for ILS procedures.
I don't think it's a great idea to fly ILS routinely at 60 kts --
as someone pointed out, the margin over stall is much lower and
the configuration changes needed for correction much larger than
at 90 kts. OTOH, a practice of never retarding the throttle
until over the threshold (as I believe Rick Durden suggested)
would IMHO definately be a bad idea on a shorter runway (say
5000-6000 ft) w/ a tailwind.

And my advice to instrument students is: make sure you actually
land out of a good number of ILS in a number of different
circumstances,
preferably ILS in IMC or at night. For that matter, make sure you
land out of a variety of approaches.

Cheers,
Sydney

(Snowbird) wrote:
As far as I could tell, it didn't do a thing to my landing roll.

You may not have noticed the increase, but physics is physics. Most
spam cans touch down at about 50 kts, which means a 10 kt tailwind
increases your touchdown ground speed by 20%. Basic physics says that
will increase your ground roll by 44% for the same amount of braking
effort.

Everybody should try some downwind landings, if only to see just how bad
an idea they are. The problem is how. I don't like doing them at
uncontrolled fields, because you're going against traffic. The best way
is to find a towered airport at a time when there's nobody else around
and ask for the downwind runway.

In article ,
(Snowbird) wrote:
I don't know about a Skyhawk, but FWIW, our former home airport
used to have only 1 ILS, to Rwy 8 which meant if low wx combined with
wind, one might be landing with a tailwind (prevailing winds from
west in these parts). As a training exercise, one time I kept my
speed up to 90 kts over the threshold. I didn't run off the runway,
but I was durn close to my "go around!" point before my plane
decided to quit flying and settle down. I definately landed on
the last 3rd of a 6,500 ft runway. Dunno what the tailwind was --
nothing too startling (10-12 kts?)

As you discovered, a 10-12 knot tailwind is indeed pretty startling.
Most people don't realize just how much effect a relatively small
tailwind has.

I happen to have a Beech S35 POH handy here. For some mumble
combination of weight, temperature, and altitude, the distance over a 50
foot obstacle goes up from 900 to 1400 feet with a 10 kt tailwind. The
graph doesn't go beyond a 10 kt tailwind; I can only assume Beech
figured nobody would want to try a landing with any more :-)

By eye, it looks like the tailwind guide line goes up at about 2-3 times
the slope of the headwind guide line (there's nothing about the shape or
slope of those curves which is model specific).

For linear (de-)acceleration, the distance used goes up by the square of
the ground speed. You normally cross the threshold at maybe 70 kts in a
typical spam can. Crank that up to 90 at the end of an ILS, and you're
using 65% more runway. Add a 10 kt tailwind, and you're using 105% more.

The chart doesn't say anything about how much to increase the distance
by on a wet runway. Or because (as others have pointed out), it's night
and your visual cues suck so your landing isn't as good as it could be.

On Wed, 21 Jan 2004 21:56:10 -0500, Roy Smith wrote:

The
graph doesn't go beyond a 10 kt tailwind; I can only assume Beech
figured nobody would want to try a landing with any more :-)

I believe that at air carrier airports (and, from personal experience, at
BOS) ATC may continue using a runway with up to a ten knot tailwind.

My first tailwind landing ever was done out of an ILS at BOS with about a
ten knot quartering tailwind. But they have long runways (and I needed to
be at the far end anyway to get to the GA ramp).


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Snowbird wrote:

Unfortunately, since many training ILS are done to a missed
approach, landing from an ILS isn't something at which some
instrument pilots get a lot of practice.

That's why I do all my training approaches to a TGL. Which of course, means I
don't get a lot of practice at missed approaches. I guess I ought to mix it up a
little.

Dave
Remove SHIRT to reply directly.

Any thoughts as to why Approach Plates do not list the time for an
approach speed of 75 KIAS?

In a previous article, said:
Any thoughts as to why Approach Plates do not list the time for an
approach speed of 75 KIAS?

Because it's hard to land when you've got a Dash 8 embedded in your
backside?

--
Paul Tomblin http://xcski.com/blogs/pt/
.... industry giant Microsoft Corporation... a company that has become
successful without resorting to software testing...
-- Unknown, rec.humor.funny