The Two Fundamental Concepts that Greatly Simplify NDB Approaches

It was an instrument lesson and an actual approach. We were flying a Piper Arrow into the Monterey Peninsula Airport just north of the famous Pebble Beach Country Club. The localizer was out of service. The only available approach was the NDB  (non-directional beacon) approach using the outer compass locater nestled up against  the outer marker on the breakwater where the peninsula met the Pacific. Flying the  Monterey Bay coast is one of the most beautiful sights in aviation. Above the cloud 

layer the sky is dazzling. Green and brown hills push up through the seemingly  perpetual low stratus more than a thousand feet above the cloud tops. On that day, the  tops were less than 1,000 MSL. 

One fundamental principle of NDB approaches is to fly the course that takes you from  the radio beacon to the missed approach point. The other fundamental principle is that  the accuracy is limited by the accuracy of your gyrocompass. Any drift or 

uncompensated deviation degrades your ability to fly an accurate course. 

The NDB approach requires that you use your gyrocompass for heading reference and  your radio compass (automatic direction finder, a.k.a. ADF) for orientation. The fatal mistake is to simply follow the needle. The seductive part of an NDB approach is that 

half of the time, following the needle works just fine. That half is until you pass over  the beacon. Once your needle points back at 180°, all the radio compass tells you is  that your tail is pointing at the radio beacon. You could be flying in any direction. 

I decided to let Ralph try the approach and told Approach Control that we would execute a missed approach at or before the missed approach point (MAP). Ralph and I  had talked about NDB approaches. I was not sure he understood them. Here was a 

place where a mistake could be fatal. So during our procedure turn outbound and still  above the clouds, I told him to be prepared for me to take over and execute the missed  approach. 

We descended into the clouds. Shortly after passing the NDB, we were 30° degrees  off course and headed into high terrain. I asked Ralph what heading would get us to  the airport. He could not tell me and said we were doing just fine. He started to argue 

with me about flying a missed approach and who should be flying. I applied full  power, retracted flaps and gear, and told ATC that we were missed. Ralph decided I  was serious and capitulated. Once we were on top Ralph stared at the mountains and 

turned pale. © Copyright 2008-2010 Douglas W. Daniel. All rights reserved. 

Assume the course from the NDB to the missed approach point is 100°. Make it easy by assuming that the inbound course to the NDB is also 100°. Fly a 30° intercept to the inbound course. This would be either 70° or 130° depending on the approach procedure. If it is 130°, your heading is 30° to the right of the inbound course. Your ADF would read 30° to the left of straight ahead or 330° when you intercept the course that you want to follow. If you are two miles or more from the NDB, start the 

turn inbound just a few degrees early so you can roll to wings level just as the ADF centers. Initially fly the magnetic heading shown on the approach procedure. In a few moments the ADF will start to move to either the right or left. It always does.

To interrupt the narrative, how do you know when you are on the path that takes you over the NDB to the airport? The answer is when the ADF needle is off to one side and the gyrocompass if off by an equal angle to the other side. Earlier your 

gyrocompass was off by 30° to the right and your ADF was off by 30° to the left so you were on the course but not on the proper heading. We'll try to nail this down next. 

Continuing to track inbound to the NDB, fly trial headings and watch the ADF. Your first try is the heading on the chart. If the wind blows you to one side, turn back far enough that the ADF is pointing to the other side. Suppose the wind blows you to the 

left until the ADF points to 005°, turn right until it points to -005° which is really 355°. This would require a 10° turn changing your heading from 100° to 110°. Hold that course until the ADF moves left to -010° or 350°. If the ADF moves right, then 

you did not turn far enough, but let's say you did. Once again the radio compass is off an equal but opposite angle from the gyrocompass. You are on course but not on the proper heading. You know that the correction angle is between zero and ten degrees because zero was taking you to the left of the inbound course and ten would have taken you to the right of it if you had continued. If the wind compensating angle is between zero and ten degrees, then the heading to fly is between 100° and 110°.You 

may as well try half way between. That would be 105°. It won't work either exactly, so keep refining your heading. 

This is the procedure that you follow all the way to the missed approach point. Once past the NDB your corrections are left or right of straight back rather than straight ahead. 

To put it in a nutshell, for an NDB approach or any other kind of approach, fly headings, don't chase needles.

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NDB Approaches Made Easy

The NDB approach is the oldest instrument approach and the most difficult to fly. For
me, it is the approach of last resort. A non-directional beacon is a very simple AM,
low power radio transmitter located near an airport. It sends out a Morse code signal
that you can listen to for identification. That's all; no azimuth or range information.
The instrument that tells you what direction you are headed is the gyrocompass after it
has be aligned with the magnetic compass. The instrument that tells you where the
NDB is relative to your airplane is the automatic direction finder (ADF). The ADF
looks like the gyrocompass but the compass rose has a different meaning. 360° means
straight ahead of the airplane, 90° means to the right, and so on around. You have to
use both of the compasses to fly a successful NDB approach.

Let me set up a hypothetical and straightforward NDB approach. Assume that the
NDB is three nautical miles from the missed approach point (MAP); the wind is from
the northwest at 14 knots; the approach speed is 100 knots; the minimum descent
altitude (MDA) is 350' MSL; and the final approach course is 360° magnetic. The
approach procedure tells you to pass over the NDB at 950' MSL. The NDB also
serves as the final approach fix (FAF).

Knowing all this, you do some mental arithmetic. The 14 knot wind has a 10 knot
crosswind component and a 10 knot headwind component. We can see that the ground
speed on final approach will be 90 knots. Fortunately 90 knots is 1.5 miles per minute.
So if you must go 3 miles from FAF to MAP, the approach will take 2 minutes. The
FAF altitude is 600 feet above the MAP altitude, so the final approach vertical speed
should be 300 feet per minute (fpm).

Let's start after you have descended to 950'MSL and have turned inbound to intercept
the final approach course. You fly a heading of 30° until the ADF reads 330°. The
airplane is now directly south of the NDB. A turn to 360° puts the plane on a bearing
directly to the NDB and both the gyrocompass and ADF read 360°. As the airplane
approaches the NDB the crosswind component blows you off course to the right.
The ADF tells you that the plane is off course by pointing to the left of straight ahead
by a few degrees. You cannot turn the airplane by those few degrees and head directly
toward the NDB again and hope to intercept the inbound course because the wind will
just blow you off course again. You know that you need to turn into the wind to some
degree if you are to find the crab angle that will keep you on course to the NDB. If the
ADF told you that the NDB is 5° to the left, you need to turn to a course that is more
than 5° to the left of the NDB. Read this next paragraph very carefully. It is tricky.

You know that you must turn into the wind to compensate for its drift. The ADF told
you that you have moved to the right relative to the NDB. Therefore you must turn to
the left. If you turned 5°, you would be pointing directly toward the NDB. You also
know that you must be heading to the left of the NDB to compensate for the
crosswind. If you did not move any closer to the NDB during your turn, you might
turn 5° to the left of the NDB and be on a ground track that would take you directly
over the NDB. But you have moved closer to the NDB and you want to intercept the
inbound course before you get to the NDB so you have more time to fine-tune your
inbound heading.

You turn the airplane 15° to the left. Both the ADF and the gyrocompass respond. The
ADF changes from 355° to 010°. The gyrocompass changes from 360° to 345°. You
want to stay on that heading until intercepting the inbound course. You would like to
see the ADF change from 010° to 015°. You monitor the ADF to see if it starts to
swing back to the right. If it doesn't, you need to increase the correction angle. If the
needle does swing to the right, you will be on course when the ADF points the same
number of degrees but in an opposite direction from the apparent error on the
gyrocompass. In this case, the ADF would read 015° and the gyrocompass would read
345°. Once you are on course, turn right to a heading of 355°. That is based on the
belief that a 5° correction to the left is the proper drift correction angle. You continue
to fine-tune your approach heading all the way to MAP at MDA.

Here is a mental trick that works for me that you might try: When looking at the ADF,
I think of 345° as -15° or as 15° to the left of straight ahead. I visualize it as one big
mark and one small mark to the left of straight up.

As you approach the NDB, you stabilize the airspeed at 100 knots indicated airspeed
(KIAS). When the ADF starts to be extremely sensitive, you know that you are very
close to the transmitter and simply fly what you believe to be the best heading. When
the ADF suddenly reverses itself, you note the time or push a timer button. You
reduce power to a setting that should yield a 300 fpm descent. You continue to track
toward the airport, maintaining a very constant airspeed. You adjust the power as
needed to establish your 300fpm or slightly greater descent.

Ideally you should be at MDA before you reach the MAP, otherwise you may never
descend to MDA. You are very careful to never descent below MDA.
When the timer indicates that the plane has flown for two minutes past the FAF, and
you do not have the airport environment in sight, you must execute the missed
approach procedure.

Doug Daniel is a long time pilot, flight instructor, software engineering manager and author. His department developed the software for the out-the-window-displays for the space shuttle, F-117, RS-71 and numerous other exotic airplanes. His writing focuses on flying techniques designed to make flying easier and safer. If this was interesting, visit his website at http://PrivatePilotTrainingOnline.org .

 

Is The Crosswind Too Strong?

There are two ways to know if a crosswind is too strong. One is to land and see if you skid off the side of the runway or ground loop. The other is to cross control the airplane before landing to see if you can align the airplane with the runway. I prefer the second technique. 

When you use your rudder to align the airplane with the runway and the ailerons to move the airplane laterally over the runway, you are cross controlling the airplane. This is a technique not used often in flight, but a very useful one to master.

Some pilots advocate flying wings level in a crosswind and kicking the rudder pedal vigorously the instant before touchdown to get the airplane pointed in the right direction. I have even seen this technique described in how-to-fly books. But frankly, this is one of those ideas that sound good if you say them fast. With this technique, you just don't know if you can get the nose pointed down the runway until you land, nor do you know if the crosswind will blow you off the runway before you're on the surface and under control. So if your life insurance is paid up and you don't have an aviation exclusion clause, you might try the old kick-and-hope trick.

There is an exception. If you are flying a nose wheel equipped airplane with liftkilling spoilers - which means you are flying a heavy airplane, not a light plane - then you can deploy the spoilers fully the instant you touch down and let the plane swivel

toward the far end of the runway. I would refer you to that now famous Lufthansa crosswind landing. Its URL is http://www.youtube.com/watch?v=z42fchrzhHY . As you can see, even that technique requires some rather precise timing. I have seen some videos of the A380 and some B474s successfully using this technique. They were flown by multi-thousand hour test pilots. I don't think it is in the cards for someone flying a light plane.

Passengers find cross controlling disconcerting. All of us like the floor to be directly beneath us and the seat to feel level. Cross controlling to align the wheels with their direction of travel requires that the upwind wing go down and that the pilot press -sometimes vigorously - on the downwind rudder pedal. Suddenly the floor is no longer level and the seat sits at an angle. This is all very upsetting to the passengers.What to do?

I recommend practicing entering the cross controlled state just as you start to raise the nose to land. This is the optimal technique and only requires slightly more skill than the procedure I describe a little further on. 

The wing loses lift when it is cross controlled raising the airplane's stall speed slightly. If the airplane cannot be cross controlled enough to get the airplane properly aligned, applying power immediately and returning to a wings-level, coordinated flying condition will lower the stall speed again and get the airplane climbing. This would not be a good time to botch a go-around.

This technique minimizes the passengers' exposure to cross controlled flight. Nevertheless, it is better to have a disconcerted passenger than a bent airplane. So if you are not the compete master of the cross control at the last minute technique, cross control while you are still in your pre-landing glide. If you cross control when you are a hundred feet above the surface, you have enough time to see if the airplane can be aligned with the runway before you have to start concentrating on the landing itself. If not, then you have plenty of time to smoothly transition back to wings level and execute an un-hurried go-around. This technique is the easiest and therefore the safest. But it is the most disconcerting to the uninitiated.

So let your passengers know before you do it, that this is a necessary and safe procedure. An important point here is that you should keep cross controlled all the way through the landing and during the roll out.

A lot has been said and written over the years about crosswind landings. It all boils down to having your wheels pointed in the same direction you are traveling before you touch down and knowing if you can while you have enough time, altitude and airspeed to easily make a safe go-around.

If you want to learn more ways to refine your flying skills and get a  *free report* on how even a PC-based flight simulator can help you fly better, ask his experts a question or just get the free report, click  here now => http://PrivatePilotTrainingOnline.org.

Flying through Thunderstorms

The old, grizzled pilot was asked, "How should I fly through a thunderstorm that I could not avoid?"

The answer he wanted to give was either, "You can't." or "Don't try."

But the question needed to be answered. Here is his advice:

Just about the only way to inadvertently get into a thunderstorm is by flying instruments in clouds with embedded thunderstorms and without either weather radar equipment onboard or ground-based weather radar available to your air traffic controller. Let's assume this is how Fate dealt you such a poor hand.

The biggest danger in a thunderstorm is structural failure. My advice is: don't do anything that helps the thunderstorm tear your airplane to pieces. When you realize that you are in trouble, the very first thing to do is to slow down. I mean not just to maneuvering speed but much slower than that. Slow to what is known as 'slow cruise' - the speed that you use in holding patterns. This will be fairly close to the best rate of climb airspeed for your airplane. Slow cruise is slow enough to minimize the adverse effects of turbulence and fast enough to keep your controls responsive. Consider putting your wheels down. This will help you stay slow. Most airplanes are not as strong with flaps out, so don't use flaps unless there is no restriction against it in your pilot's handbook for the airplane.

The reason to slow down is that the higher your airspeed, the greater force turbulence can impart on your airplane. That destructive force comes in the form of lift. Remember that lift is proportional to the speed of the airplane squared. Slow is good.

Too slow is not good simply because the last thing that you need is to stall and spin when you are in a thunderstorm.

There is an adage in aviation that says a pilot's priorities are aviate, navigate and communicate, in that order. I agree. Certainly your most important task is to fly the airplane. However, you need all the help you can get. So tell air traffic control (ATC) that you are in trouble and need help. Ask them to vector you out of the thunderstorm. Tell them that you cannot maintain the assigned altitude - because you cannot. Ask them to vector you away from high terrain. Be aware that your inability to maintain altitude can easily put you in a position where you cannot communicate with ATC for some period of time.

The intensity of rain in a thunderstorm can be truly phenomenal. Quite possibly your engine or engines can start to ingest a great deal of water. This water can turn to ice in your carburetor especially at high altitudes and low power settings. When you apply carburetor heat, the mixture enriches forcing you to lean the engine or risk fouling the spark plugs. Tuning the engine is an integral part of flying the airplane, your most important task.

The updrafts and downdrafts in a thunderstorm can far exceed a general aviation airplane's ability to climb or dive. So just ride them out. Don't start building airspeed by pushing your nose down to stay at your assigned altitude in a strong updraft. If you get caught in a strong downdraft, go to your best rate of climb airspeed at full power. You will still go down - just not as fast and not so far. When the downdraft subsides, you will start climbing back to your assigned altitude. If you have oxygen and perhaps if you don't, ask ATC for a higher altitude so you will have a greater margin of safety when you enter your next overpowering downdraft. If ATC will not grant you a higher altitude, do not be afraid to declare an emergency and tell ATC that you are going to a higher altitude.

There are two things that you should remember here. First, if the FAA issues a violation, it is better to argue in court that you needed that higher altitude than it is to have the surviving members of your family argue in court that the FAA should have cleared you to a higher altitude. Second, when you go high without oxygen, you get so stupid that you don't know how stupid you are. Having said that, when you are at 10,000 feet facing 12,000 feet peaks and a known thunderstorm behind you, the options start to narrow. For me, it is better to face hypoxia than certain death.

To sum it up: Plan your fight and check your weather well enough to know that you are not going into a thunderstorm.

If, by some fluke of nature, you end up in a thunderstorm that was not predicted and you could not see, then

1. Slow down.

2. Remember that flying the airplane is your most important task.

3. Get out of the thunderstorm as quickly as possible.

4. Keep going straight with wings level while you ride out overpowering up and downdrafts.

5. Tell ATC.

6. Ask for help.

 

If you want to learn more ways to refine your flying skills and get a *free report* on how even a PC-based flight simulator can help you fly better, ask his experts a question or just get the free report, click here now => http://PrivatePilotTrainingOnline.org.