Clearly, altitude is one thing a pilot needs to think about seriously. A recent study of 1966 National Transportation Safety Board general aviation accident data showed that 63 percent of fatal maneuvering accidents occurred during personal flights. The majority of these accidents resulted from buzzing or unauthorized low-altitude flight.
What makes these statistics tragic is that pilots can prevent these low-flight accidents. Most of them took place during day VFR conditions, when pilots have the freedom to choose the altitudes they fly. The statistics show that too many pilots are not choosing wisely. They also emphasize the need for instructors to make sure their students understand not only the importance of choosing a safe altitude but, more specifically, how to choose a minimum safe one.
The Regs
Students want you to give them the exact definition of a minimum safe altitude (MSA). Unfortunately, the answer isn't always clear cut. The best you can do is explain the things to think about when selecting an altitude. This sounds simplistic, but it's an invaluable lesson. Your students are new to flying and they want and need to hear how you - a more experienced pilot - pick an altitude.
Federal Aviation Regulation 91.119, "Minimum Safe Altitudes," is a good place to start this discussion. It says a minimum safe altitude is one that allows a pilot to make "an emergency landing without undue hazard to persons or property on the surface" if the engine quits. The regulation doesn't give any numbers - the pilot has to pick an altitude that will allow him to meet the regulation's requirement regardless what terrain he's flying above.
FAR 91.119 does give numerical minimum altitudes for flying over congested areas such as cities or open-air gatherings of people (1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft) and "other than congested areas" (500 feet above the surface, except over water or over sparsely populated areas, where the airplane must be no closer than 500 feet to any "person, vessel, vehicle, or structure").
Make sure students understand the FARs give the absolute minimum - not necessarily what's prudent or safe. For example, over water a pilot can fly at 100 feet or lower if there are no boats within 500 feet of the airplane. This is legal, but it's not safe. If the engine quits, you won't have much time to deal with the emergency let alone think about gliding to shore. However, the true value of FAR 91.119 lies not so much in the numeric minimums it gives, but in the issues it raises.
This elegant regulation works because it asks pilots to answer two inescapable questions - Where would I land if the engine quit right now? and Could I hit something at this altitude?
These questions are the foundation for selecting a safe altitude. Of these two, obstacle clearance takes precedence, and you can incorporate this lesson into other subjects such as planning a cross-country flight. Have the student start with the sectional chart's maximum elevation figures (MEFs) along the proposed route and work up from there.
A safe altitude will be at or above the MEF and comply with FAR 91.159, the VFR hemispheric rule. If the route passes through mountainous terrain but is not near any mountain peaks, students will find the MEF to be somewhat excessive. In this case, teach them how to examine the spot elevations along the route to ascertain a suitable altitude. If there's a possibility of a strong wind over the mountainous terrain, have them add an extra 2,000 feet to their altitude to keep them above orographic turbulence.
If students plan to fly over open, flat terrain, they might be tempted to fly at a lower altitude. However, statistics show that wires pose a serious threat at low altitudes, so flying at or above the MEF is still the safest bet over flat terrain.
Next, students need to learn how to answer the question "Where would I land if the engine quit. Students should understand that running out of gas is the primary cause of engine "failures," but mechanical failures do happen and they need to be prepared.
A successful emergency landing depends on numerous factors, and altitude is the most important. First, a safe altitude allows adequate time and distance to glide to a suitable emergency landing site. To select an appropriate altitude, have students work from the ground up. For example, ask them to identify potential emergency landing sites along their proposed route. Airports are ideal, but dirt strips, lightly traveled roads (as long as they're free of adjacent power lines), and flat, open fields also work.
With their sites identified, have students measure the distance from these sites to their proposed route. They should understand that in flight they will have to estimate this distance, just as they do during a simulated power failure. They should always be looking for areas with emergency landing site possibilities.
Finally, have students use the glide distance chart in the pilot's operating handbook to figure out how high they must fly along their proposed route to be able to glide to the landing site. Remind students to plan their glide so they will have at least 1,000 feet of altitude when they arrive at the emergency field, so they have enough time at a safe altitude to set up their landing. If the route is over open, flat land, emergency landing sites should be plentiful. The cruising altitude doesn't have to be as high as it would if the route were over heavily wooded areas, which might require a longer gliding distance to reach an open, safe landing site.
Students don't need to perform this exercise for every cross-country flight. The idea is to make them think about their answers to the two questions - and to think about their proposed route. If students have to fly at 15,000 feet to have the necessary glide range, they'll need to reroute their flight to put emergency landings sites closer at hand. Ultimately, students should understand that more altitude equals better obstacle clearance and, in an emergency, more time to think, plan, communicate, and prepare.
Training
During primary flight training, students fly two different types of air work. High-altitude work includes such maneuvers as steep turns, stalls, and slow flight. Low-altitude work includes such ground-reference maneuvers as turns around a point. The private pilot practical test standards says 1,500 feet AGL is the minimum safe altitude for high work and 600 feet AGL for low work.
Depending on the situation, these minimum altitudes may or may not be appropriate. Teach students to evaluate their altitude - or the location where they fly the maneuvers - by answering the cross-country questions, "Where would I land if the engine quit right now?" and "Could I hit something at this altitude?"
Fly Higher
Minimum altitudes are just that, the lowest altitudes your students should ever want to fly. However, they should know why they might fly at an altitude much higher than the minimum. No discussion of minimum altitudes would be complete without covering some of these reasons.
For example, a higher altitude gives airplanes a faster true airspeed for the same fuel flow. It gives better terrain and obstacle clearance. It gives them a better field of view, which makes it easier to spot landmarks and airports. And it gives their communication and navigation radios more range and better ATC radar coverage.
Teaching minimum safe altitudes is a challenge because the variables are not constant. Not only do they change from flight to flight, but they change during the flight as the airplane flies over changing terrain. Because our students are with us for a short time relative to their entire flying lives, it's an instructor's responsibility to teach them the things they should think about when picking a minimum safe altitude - the risks they must weigh. In the end, if we are successful, they will feel quite comfortable explaining the similarities between a pilot and an insurance company.
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