To: DIPLOCAT Judith Bradt
fork and spoon time.
thought of it in terms of how many feet that means one is off
before; I was still sitting there thinking: "That's 1/6 of
a mile drift per minute, when the airplane is going 1.5 nm in
that minute..." I can see how it becomes a pretty small amount
between the FAF and the threshold. On the approaches I've been
flying, the NDB is on the airport. It's about (3 minutes at 90
knots, so...uh.1.5x3...) 4.5 miles from the point where one leaves
the final leg of the procedure turn for the inbound leg to the
beacon. For every minute, in your example, one would drift 1 foot
for every nine flown. With 20 knots crosswind, would that make
the ratio 9:2, though, wouldn't it? That would mean in 4.5 nm,
I might drift 4 nmif I only held the published heading, wouldn't
it? And if visibility or ceilings are close to minimums, I might
have to miss the airport...
Your idea about
turning back onto the published heading every so often to check
things would work if I could establish heading precisely and keep
everything else stable for long enough to check, interpret, and
respond as needed to whatever I determine the instruments are telling
me. So far, the combination has been difficult.
are a great deal like a knife fork and spoon: each has an appropriate
First of all,
holding the inbound course as a heading after passing the NDB is
useful ONLY when the NDB is located off-field. It doesn't make any
sense whatsoever to use that technique when the NDB is located on
the field, as the NDB is the missed-approach point. The technique
that I use is employed only when the NDB is the final approach fix
(FAF) -- not the MAP.
In your example,
you used a 20 knot (I assume, direct) crosswind, stating that you
might drift 4 NM in flying 4.5 NM. No no no. In flying 4.5 miles,
you'd only drift ONE mile. (Look at the ratios: 9:2 = 4.5:1 ) Secondly,
you can't land a Cherokee in a 20 knot direct crosswind, if my memory
serves me correctly, the max allowable crosswind is 15 knots, isn't
it? So, you'll have to use a circling approach: thus, higher minimums
would apply in any case. But in your example, you're approaching
an airport where the NDB is located ON THE FIELD -- so you'd just
navigate as normal while inbound to the station. Worrying about
drift (the ratio I gave you) applies only where the NDB is located
OFF the airport.
In the case
where the NDB is located off-field, and is the FAF, the technique
of periodically turning back to the outbound course (FAF to MAP)
as a heading is useful only to check your amount of drift during
the final approach segment.
is that with station passage, too many pilots will NOT hold a heading
within a 1.5-2 mile radius of the NDB and try to chase the needle
to hold their course. (A great deal of ADF navigation is having
the patience to sit on your hands for a few minutes and do nothing
at all.) Thus, when the pilot is chasing the needle and passes the
station, they'll usually make some radically drastic and inappropriate
heading changes while yet fairly close to the station. The results
are disastrous, particularly if the pilot has to make altitude changes
at the same time.
a student to cross the station and DELAY making a heading change
to re-intercept the outbound course (FAF to MAP) allows them time
for the needle to stabilize somewhat. Then, 10-15 seconds after
station passage, a heading change can be made to re-intercept the
outbound course to the airport. Every 30 seconds after that, however,
I taught that the pilot should turn to a compass heading equivalent
to the outbound course (FAF to MAP) to check that they haven't flown
THROUGH their course -- WHICH IS NOT A REAL GOOD IDEA WHEN YOU'RE
GETTING CLOSER AND CLOSER AND CLOSER TO THE GROUND.
a check of their position relative to the outbound bearing, I had
the pilot return to their heading to re-intercept the outbound course,
only to check again in 30 seconds. (Don't forget that WINDS CHANGE
VELOCITY, that is, speed and direction, WITH CHANGES IN ALTITUDE.
Therefore it follows that as you get closer to the ground, the amount
of corrections you'll need to intercept or maintain a course is
going to change -- OFTEN RAPIDLY. Thus the technique of returning
to your outbound course as a heading is particularly useful for
it allows the individual to check and re-check drift and position
relative to the outbound course bearing while flying FAF to MAP.)
Once the pilot
intercepted the outbound course (FAF to MAP), I'd have them hold
a wind correction angle equivalent to ONE DEGREE PER EVERY FIVE
KNOTS OF DIRECT CROSSWIND as a starting point.
This is the
opposite of what the airlines teach. They don't want ANY turns after
crossing the station. Hold the outbound course as a heading. The
amount of lateral drift is minimal and well within protected airspace
My point is
this: don't make any radical changes in heading when you're close
to the station, inbound OR outbound. Many student instrument pilots
(and their instructors) try to make non-precision approaches precise:
in contrast, the airlines adopt techniques that are within tolerances
and are more realistic.
been working out sample solutions to the ADF problems, but at
large deltas I tended not to get confused...When I get there,
I'm going to want to leave some correction angle in for the wind,
so I'll maybe turn 260 and see what happens. Any glaringly dangerous
logical processes there?
Well, I commend
you for starting to think of ADF navigation with respect (and relative)
to the tail of the needle. That's the first indication that you're
learning, or at least you're reading what I'm sending you.
In fact, it's
the first indication of ADF smarts on your part. That's what the
pros do. Keep thinking in those terms. As for the rest of your thought
MB=RB+MH is intended to get you to start thinking about the needle
of the fixed-card ADF instrument RELATIVE to your accurately-set
compass card, what I assume you're referring to as the HI. Pros
simply overlay the ADF needle on the compass card, and the rest
is easy, relatively speaking.
teach the NDB as a necessary evil, and don't really emphasize NDB
navigation and holding enough -- or early enough in instrument flying
-- because of the over-reliance on VOR and ILS approaches. As I
stated before, YOU CAN'T FLY A PRECISION APPROACH UNTIL YOU'VE MASTERED
NDB NAVIGATION, HOLDING AND APPROACHES AS THE PRINCIPLES ARE ALL
mastering the NDB facilitates everything that you do in a precision
approach. You think of the glideslope and localizer in the same
way that you do the final approach segment of an NDB approach (opposite
angles are equal).
All the mental
gymnastics of MB=RB+MH are dangerously distracting. Because of this,
I STRONGLY recommended that you get into an airplane equipped with
an RMI -- thus eliminating the need to distract yourself mentally
trying to figure out what bearing you're on, etc, etc while flying.
What matters is WHERE you are, WHERE you're going, and HOW you get
there. A controller will never ask you what bearing you're on; the
only time that being on the exact bearing matters at all is when
you're holding on an NDB or flying an NDB approach. Even then, if
you're like 99% of the pros, you'll only be able to bracket the
bearing while holding or on approach.
True, the brackets
are small, and the distance from the bearing is measurable in terms
of hundreds of yards, not miles.
asked me what I think about I think about your thought processes,
let me state this:
of successful ADF navigation and approaches is in realizing that
in geometry, opposite angles are equal."
Too much emphasis
is placed on the RB+MH=MB -- people get too wrapped up in the mathematics,
particularly in flight. If you can just mentally overlay the needle
on your compass card, more than 75% of the battle is won.
this, you make the shortest turn to put the head or the tail of
the ADF needle in the upper half of the ADF instrument. Once you're
close to intercepting a bearing and have turned to intercept and
fly inbound/outbound, it's a matter of balancing needle drift/displacement
with an opposite correction angle.
all takes me a long time to work out, however -- and it's very
distracting to try and do it in flight, let alone on the ground.
I believe this is the reason why studying and practice and studying
and studying are recommended.
Yes -- exactly
what I've been talking about.
I know and remember well the frustration of trying to learn the
ADF and in doing NDB approaches. I share your frustration with the
mental gymnastics. I knew what was coming and, because I like you,
wanted to spare you this frustration by recommending flying an HSI
and RMI equipped airplane. Many, if not most, of all people who
quit an instrument rating course do so when the lesson plans come
to ADF navigation and NDB approaches. Most people who fail their
instrument check ride do so because they really haven't learned
the ADF, and can't do NDB approaches or NDB holding. It plagues
the airlines, too, because many of the people I've flown with simply
have never mastered the NDB -- and many of them have worked as Instrument
truth of this matter is that I probably couldn't fly an NDB approach
using a fixed-card ADF. Well, I could, but not without some difficulty.
But it's that very distraction of the mental gymnastics which make
the flying difficult.
Stay with it.
Don't just try to get through ADF navigation -- break through it.
It's a good fight.
And keep thinking
in terms of the tail of the needle.
the frustration well that you are now feeling. Don't worry: you'll
get over it. I don't mean that you'll not feel frustrated -- I just
have the feeling that you'll stick with this until you master it.
You're that type of pilot, I believe. If you're not, it will come
as a shock. For the moment, I'll not offer any advice about flying
the ADF. When you're ready, let's exchange a few letters about what
you DO understand about it, and I'll try to fill in the missing
blanks, if any.
The truth is,
Judy, that if you can't fly an NDB approach, you probably can't
fly a precision approach. The elements are all the same. That's
the bad news.
The good news
is that you probably know already how to navigate by and use the
ADF but just don't realize it. Non-precision approaches are tough.
Of those, the NDB is the toughest nut to crack. You can do it. And
you're so close to finishing, too. I listened to the new president
of Honda Motor say that, at least at his company, sucess is 96%
failure. So why should you be any different?
things like addition, subtraction, left, right,inverses, and simple
multiplication. To be as positive as I can muster at the moment,
these things are elements of flying that I find occasionally pose
me while I tear my hair out and step outside for the gulp of air
that will precede a primal scream.
I DO know the
feeling. I spent an hour breaking light bulbs and bottles, crushing
cans and chasing chickens to vent my frustration with a particularly
mean FRASCA simulator.
exercise in the meantime is to make up a dummy ADF and HI, and
work through some examples of "where am I, what do the instruments
read, and where would I have to turn" to get better at this.
This is a valuable
exercise. Don't neglect it.
it that I continue to take up activities at which one must continually
work to improve, perfect, maintain and practice skills, rather
than ones for which one can be permanently certified once and
never have to re-prove or -qualify? I suppose I would be having
less fun if I had an avocation that did not give me cause to shout
with frustration inside my car as I hurtle down Sudley Road considerably
above the speed limit.
If this was
easy, then everybody would be doing it, and doing it very well,
right? Then, the problems you're having right now would mean, what,
that you're a moron? So, what is your problem? ARE you a moron?
I didn't think you'd feel this way about yourself. So you must be
Judy, I haven't
met a good pilot yet who didn't have some threshold they had to
crash over or through at one point or another in their training
and education. Any idiot can eventually drive a golf ball 300-400
yards. It's the skill-development and practice which makes the difference
between a 80's handicap and a hacker's 200. I've seen grown, mature
men wrap golf clubs around trees in frustration -- and they're NOT
learning skills which will someday preserve or save their lives.
The truth of
the matter is that you already know how to navigate using an ADF
-- you just DON'T realize it. If you know the basic fundamentals
of boat handling, you already know how to navigate using an ADF,
just as an example. Even more basic, what you've already learned
about flying approaches (VOR, LOC and ILS) applies to NDB approaches:
the ADF is a slightly different way of looking at the same information
that a VOR provides. Change your perspective, and you're Columbus
of the New (Instrument) World.
you manage not to tell me how wonderful HSI's are, and how frustrated
people should not get in their cars and drive anyplace? Thank
Actually, I'll pretend not to be insulted about caring for you,
and being told not to. And in this case, it's RMI, not HSI.