OK, here's a riddle. Name a part of the airplane that is essential for safety but is used only when the airplane is not flying. Let's see. How about tie-down rings? No, they are a safety issue only if we leave a rope attached to one and we try to tow the ramp along with us. Ah! I've got it! It's the tires!

Sound, properly inflated tires with tread are essential to safe flying. Think keeping the airplane going in the right direction when landing in a gusty crosswind is tricky? Just imagine what would happen if a tire was to fail during the process.

A tire can be pretty bad looking and still be serviceable. It can have flat spots caused by hard braking, cord can be showing, and there can be cuts in the tread. But just because a tire is considered serviceable doesn't mean that it is going to provide optimum performance. Generally a tire can remain in service if cord is showing on not more than 1/8 the circumference of the tire. Just consider that cord doesn't have the same stopping power as rubber. And, if the brakes get locked up and the cord is in contact with the pavement, things could get ugly fast.

Tires take a beating regardless of the airplane size. They are deformed upon landing both from the weight of the airplane (perhaps several times the actual landing weight) and from the sudden rotational acceleration. Add to that any side loading caused by pilot technique and the tire is truly brutalized.

So the tires deserve their fair share of attention during the preflight inspection. Installed wheel fairings make this task harder, but would we fly without checking the oil if the dipstick wasn't easily accessible? I hope not. The airplane can be rolled a few inches at a time to reveal the entire tire. Have anything that looks suspicious checked by qualified maintenance personnel. But remember that the technician's job is primarily to determine if the tire is serviceable. It's still the pilot's job to ensure safety. So don't be shy about refusing to fly if a tire is out of your comfort zone.

Tire pressure is really important and should be considered during the preflight. It probably should be checked with a gage before each flight, but that may not be practical. (Imagine the flight school where students check the tire pressure before each flight. The tire would lose 10 pounds of pressure by the end of the day.) But the pressure should be checked before flight if the airplane hasn't flown in awhile. Fleet airplanes flying frequently should probably be checked daily.

As takeoff and landing speeds increase and aircraft weight increases, tire pressures become more critical and must be checked more frequently. I used to own a Piper Navajo which was particularly sensitive to tire pressure. My preflight inspection tools included a tire pressure gage along with the fuel tester.

Simply flying from one area to another where the temperature is significantly different can cause a substantial change in tire pressure. Every 5 degree F. change in temperature will result in a 1% change in tire pressure.

Aircraft tires generally look like they are under inflated compared to their cousins on our cars. The calibrated eyeball isn't sufficient to determine tire pressure. Goodyear specifies that their tires be inflated to the range of -0/+5% of the recommended minimum service pressure. The pressure must be checked when the tire is cold.

Under inflated tires can cause lots of problems as they do their job. There is a takeoff performance penalty because they require more energy to roll. They will also wear excessively and they will generate excessive heat which can lead to damage or failure. Under inflated tires also cause excessive wear and an increased likelihood of hydroplaning. (The minimum speed for hydroplaning is 9 times the square root of the tire pressure.)

There is plenty more to say about tires but this is supposed to be an article and not a dissertation so I'll stop here. The folks at Goodyear are as knowledgeable about airplane tires as anyone and they have an excellent downloadable document available. Click here to download it from their website.

"The flight isn't over till the airplane is back in the barn." That's what my flight instructor used to say. I think he was trying to tell me that I should be careful when taxiing to the hangar and putting the airplane away. Perhaps we need to expand that to include maneuvering for landing. Too many pilots complete a successful flight only to crash on or near their destination airport.

If we take out collisions with other airplanes in the pattern and collisions with obstacles in the airport environment, we are almost always looking at a stall/spin situation. But why? Realtors like the phrase, "location, location, location." Flight instructors like the phrase, "airspeed, airspeed, airspeed."

OK, the airplane doesn't stall because we fly it too slowly. It stalls because we exceed the critical angle of attack. But if an airplane is to remain aloft, decreasing airspeed requires increasing the angle of attack. As the angle of attack increases it gets progressively closer to the critical angle of attack and therefore the stall. Once the airplane is flying within a few degrees of the critical angle of attack, any increase in load factors, such as beginning a turn or encountering some turbulence, will put it over the edge.

Of course we have to decrease our airspeed as we approach the airport and enter the traffic pattern. We also have to make some turns, deal with ATC or traffic at non-towered airports, figure out which runway is the one we're supposed to be heading to, configure the airplane for landing, run a checklist or two, brief passengers, etc. In other words, at exactly the time we have to start flying closer to the stall, we have to divide our attention among things other than actual airplane handling.

Of course these accidents only happen to inexperienced pilots, right? Absolutely not. In fact, informal analysis of many accident reports seems to indicate the contrary.

So what are some practical ways to decrease the likelihood of being involved in this kind of accident? Studying past accidents help to identify possible causes and contributing factors that all pilots can avoid. Let's look at a few real cases.

We have an accident where the airplane was over its maximum landing weight. That alone would not cause the stall, but for each additional pound of weight at a given airspeed, the wing must fly at a slightly greater angle of attack. This gets the wing closer to the critical angle of attack and decreases the safety margin. So let's make sure we always are operating within the manufacturer's weight and balance limitations. And even though we are within the limits, let's be particularly aware of the added risks when operating near the limits. Abrupt maneuvering is never good, but can be very unforgiving when the airplane is heavily loaded.

Another stall accident in the pattern involved a pilot who had a high concentration of over-the-counter cold and cough medications in his blood. These same medications have a demonstrated negative effect on performance and produce drowsiness. This also won't cause a stall but will make it difficult to concentrate and would certainly cause a delayed reaction to the onset of a stall. Let's be sure that we are as sharp as possible for our flights. Drugs, legal and otherwise, along with alcohol, dull our senses and slow our reaction times. Taking medications and flying isn't a good idea. Whatever condition is causing us to need medication might also be a good reason not to fly till we feel better.

There is an accident where the pilot of a high performance, technically advanced airplane did not complete any factory authorized training but got a "check-out" from a local CFI who had no previous experience in the type of airplane. It is essential for every pilot to be comfortable with the characteristics of the airplane when flying near the stall. It's much better to learn about any unusual flying characteristics from someone who is accustomed to the airplane. Doing a checkout with a CFI who has no experience in the airplane just means there are two test pilots instead of one. I once decided to check myself out in a newly designed airplane. I learned that slips with full flaps made the flight path resemble that of a lawn dart. Upon further checking, I found out that I had "discovered" a well-known flight characteristic.

This applies not only to technically advanced airplanes. The light sport airplanes (LSA) can pose just as much risk to a pilot accustomed to flying a heavier single-engine airplane. So let's be sure we take whatever steps are necessary to become comfortable with any airplane we fly.

Finally there was the pilot who made an error in lining up with the assigned runway at a controlled airport and stalled when he abruptly turned after a controller calmly pointed out his error and assigned a new heading. Being more familiar with the stall characteristics, particularly accelerated stall characteristics might have prevented this accident. But studying the airport layout and having the airport diagram out as the airport was approached might have prevented the confusion that caused the pilot to execute the maneuver.

So my tips are nothing that we don't already know. Stay within weight and balance limits, don't fly when sick or taking most medications, know the flying characteristics and especially the stall characteristics of the airplane, and plan ahead for the arrival into the traffic pattern. Knowing what is safe is useless unless we practice what is safe.

Accidents discussed in this section are presented in the hope that pilots can learn from the mistakes of others and perhaps avoid repeating those mistakes. It is easy to read an accident report and dismiss the cause as carelessness or a dumb mistake. But let's remember that the accident pilot did not get up in the morning and say, "Gee, I think I'll go have an accident today." Nearly all pilots believe that they are safe. Honest introspection frequently reveals that on some occasion, we might have traveled down that same accident path.

On July 10, 2001 a Grumman American AA-1C crashed while making a steep turn to the right base to runway 26 at the South Jersey Regional Airport in Medford, NJ. The 319 hour private pilot and his passenger were fatally injured. the flight had originated from Northeast Philadelphia Airport.

The pilot was in compliance with all regulations regarding medical certification, flight review, and recent experience requirements for carrying passengers. The only possible violation was in the use of over-the-counter medications, three of which were found by toxicology testing.

According to a witness, the airplane was observed making a steep turn to a right base. During the turn, the airplane's tail abruptly went up, and the airplane entered a 2 1/2 spin to the right prior to impacting the ground. Another witness stated, " As I watched him, I was anticipating that he was going to initiate a climb since he was in no position to execute a right turn to the runway. Then he announced 'Grumman turning right base'. Personally, I was in disbelief he was going to attempt to land on runway 26." The same witness reported that the accident airplane was in a steep angle of bank, in excess of 60°, as it turned onto base leg.

There was no evidence of a pre-existing mechanical failure or malfunction.

Here is a classic case where being in compliance with the regulations did not prevent an accident. The pilot was apparently not aware of the dangers of steep turns while at a slow airspeed. He had most likely been warned of the dangers but had he ever been trained in accelerated or cross-control stalls? Perhaps he was confused as to which runway was active, initially got into the wrong place and turned steeply to get back into position. If so, could this have been avoided by advance study of the airport layout relative to his arrival route? What, if any, role did the medications play in this accident?

Stall/spin accidents occur way too frequently in the vicinity of airports. A lesson or two from a competent instructor who is familiar with the airplane and who is not afraid to practice accelerated and cross-control stalls at a safe altitude is a very good investment.

Click here to read the full NTSB accident report.

On occasion I receive an email from a college student who is doing a paper on some aspect of aviation. Sometimes the questions are obvious and I get the feeling that a quote is needed to add one more footnote. But last week I received a question that seemed simple at first but became more complex as I began to write a response. The student was doing a paper on controlled flight into terrain (CFIT) and his question was this. "Why do CFIT accidents continue to happen even with EGPWS systems on the airplane?" (EGPWS is enhanced ground proximity warning system. It is an update of earlier GPWS units in use for the past 30 or more years primarily by airlines and business aviation. The system is designed to provide a warning if the airplane is in danger of colliding with terrain or obstacles.)

The answer to this young man's question seemed simple at first. It is a warning system. If it is not used properly or if the warnings are not heeded then an accident won't be prevented. But then I thought back to general aviation where many thousands of hours are flown each year in instrument meteorological conditions (IMC) without having a CFIT accident. Sure there are some and some is too many, but most pilots don't fly into anything even when in the clouds. The possibility of having a CFIT accident if published instrument flying procedures are followed to the letter is almost nil. So we have a system installed which should not be needed and accidents still happen. Hmmm.

Flash back to the February 2009 Colgan Airways/Continental Connection crash of a Bombardier regional airliner near Buffalo, NY. The flight crew was too busy discussing how terrible their working conditions were to notice that the airspeed was deteriorating due to ice on the airplane. The airplane was equipped with a stick shaker to warn the pilots when a stall was being approached and a stick pusher to help push the nose down if a stall is imminent. Somehow, it appears that the captain did not react in a timely manner to the stick shaker and acted incorrectly to the stick pusher. Now the airplane manufacturer is being criticized by the airline for not having an additional slow speed warning system on the airplane. Hmmm.

In general aviation we are seeing lots of new high tech avionics and systems being introduced. These systems were intended to lessen the workload on the pilot and make flying safer. That isn't exactly how it's working. There appears to be an increase in CFIT accidents from non-instrument rated pilots who, relying on their GPS and terrain warning systems, continue into adverse weather and come to an unhappy end.

So at least in some cases pilots are not using their high-tech tools to improve safety. They are using them to replace the basic skill and judgment that pilots are supposed to exhibit. When this happens PIC stands for passenger-in-command. This also applies to major airline pilots who program the flight management system and then play on their laptops for hours while the airplane careens through the sky. It also applies to the general aviation pilot who needs the autopilot to fly the instrument approach because an approach hasn't been hand flown in years.

So back to the young man's question. Accidents will happen when pilots do not properly use all available resources to ensure safety.

Last spring a bought a nifty new ladder to use around the house. I can barely see the aluminum because of all the warning labels on it. I realized as I read some of the labels that people who need those warnings probably shouldn't be climbing on ladders anyway. Pilots who need more and more technology, such as another slow speed warning on an airliner, probably shouldn't be flying airplanes either.