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Are you grading yourself as a pilot?

July 18, 2012/in Tips and technique/by studentpltnews

One of the best ways to become a better pilot is easy, free and doesn’t require a flight instructor. Sound too good to be true? Hardly. In fact, you may already do it, at least in some form.

Performance on FAA Tests and in the Real World – Part 1

June 29, 2012/in Tips and technique/by studentpltnews

Pressure and Density Altitude on FAA Tests and in the Real World One of the things that you must learn as a pilot is how to determine the approximate performance you can expect out of your airplane on a given day. I say the “approximate performance” because there are simply too many variables that will […]

Are you grading yourself as a pilot?

July 18, 2012/in Tips and technique/by studentpltnews

One of the best ways to become a better pilot is easy, free and doesn’t require a flight instructor. Sound too good to be true? Hardly. In fact, you may already do it, at least in some form.

Performance on FAA Tests and in the Real World – Part 1

June 29, 2012/in Tips and technique/by studentpltnews

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Are you grading yourself as a pilot?

July 18, 2012/in Tips and technique/by studentpltnews

Be honest–how would you grade your last flight?

One of the best ways to become a better pilot is easy, free and doesn’t require a flight instructor. Sound too good to be true? Hardly. In fact, you may already do it, at least in some form.

It’s the post-flight evaluation.

Every time you fly, you probably have some gut feel about how well you performed. A solid post-flight evaluation is really just taking this gut feel to the next level. Try to force yourself to review each part of the flight–from pre-flight to landing–in a structured, disciplined way. A good time to do this is on the drive home from the airport, while the details of the flight are still fresh in your mind.

What should you review? Beyond just “that landing stunk,” replay the flight in your mind and go through a quick checklist:

Did I violate any FARs? Hopefully not, but another question might be “what do the FARs say about that situation?” Did your flight raise any questions about the regulations that suggest further study?
Did I break any personal minimums? This is often an uncomfortable question. Breaking FARs is very rare, but more than once I’ve had to admit to pushing my personal limits, whether for crosswinds or weather. If you routinely break your minimums, then they aren’t real minimums. Don’t have personal minimums? Make some. Even if they’re not extremely detailed, you ought to have some sense of what conditions are too much for you and your airplane.
Did I learn any new tricks? Sometimes we do and simply fail to recognize it. If your landings today were all excellent, ask why. You may have discovered a better approach.
Did I uncover any traps? Another place to be brutally honest. I can remember at least one instance when I accepted a clearance I should not have. It was an accident waiting to happen, but I didn’t fully realize it until after the flight. I walked through how it happened and how to avoid it next time–and I haven’t made that mistake again.
Did the weather match the forecast? Even on the shortest flight, there’s usually something weather-related to learn. On cross-country flights, I go so far as to save the weather/radar map I looked at before the flight and compare it to the one right after my flight. Seeing the difference between forecast and actual and then exploring why it changed is a great learning opportunity. You really can and should learn about weather on every flight, even if you only fly VFR.

This approach may sound obvious to some, but a disciplined review of your flying can pay big rewards. For student pilots, this is especially true, as you can learn an awful lot without the Hobbs running (which means it’s free). You might set a goal of getting 3 hours of learning out of every hour of actual flying. Some pilots go so far as to re-fly the flight on a home flight simulator or using a cockpit video camera.

The post-flight evaluation isn’t just for student pilots, though. After you earn your license, there isn’t much of a requirement to keep learning other than the obligatory flight review every two years. The safe pilot has a much higher standard than this, though. The impetus is on you to continually get better, which means every flight should be a learning experience. An honest self-critique can also be a great way to ward off complacency, which is one of the most dangerous traits any pilot can have.

Most importantly, it’s vital to do a post-flight evaluation after every flight, no matter how good it was. After all, that “good flight” may not be so good after some introspection.

Performance on FAA Tests and in the Real World – Part 1

June 29, 2012/in Tips and technique/by studentpltnews

Pressure and Density Altitude on FAA Tests and in the Real World

One of the things that you must learn as a pilot is how to determine the approximate performance you can expect out of your airplane on a given day. I say the “approximate performance” because there are simply too many variables that will affect our airplane’s performance for which we can’t directly account to get exact performance.

Pressure and Density Altitude calculations are key factors in determining performance but these can be confusing. Also confusing is the FAA’s emphasis on precise calculations on the FAA knowledge test when these values are only a part of the total performance equation. I’ll cover some of the other values in the equation in another blog post. In this post, let’s take a look at Pressure and Density Altitude.

The FAA defines Pressure Altitude as the altitude above the standard 29.92″ Hg plane. While Density Altitude is the Pressure Altitude corrected for nonstandard temperature.

Density Altitude is used in computing the performance of an aircraft and its engines. Some manufacturers utilize Pressure Altitude on their performance charts but they address the nonstandard temperature within the chart. In this way, they are actually using Density Altitude but the pilot isn’t required to calculate it.

Variation in Pressure and Density Altitude Calculations

There are several ways that Pressure Altitude can be determined depending on the accuracy and precision required by the calculation.

FAA knowledge test supplements include a table on the “Density Altitude Chart” that shows a “Pressure Altitude Conversion Factor.” The value obtained from this chart is based upon the altimeter setting and is added to the indicated altitude (the correction value will be negative when the altimeter setting is higher than 29.92″ Hg). This correction value is precise to the nearest foot and provides a reasonably accurate measure of Pressure Altitude.

The Density Altitude value obtained from this chart has some minor accuracy issues when using the standard temperature line. The lower anchor point of the standard temperature line is not set at 15° C for sea level as it should be. This lower anchor is set at approximately 16° C. This error in the chart should have less than 100 feet of error with regard to calculations.

There is a precise and rather involved formula for computing Pressure Altitude with exceptional accuracy. It can be used to calculate the Pressure Altitude out to several decimal places if needed. In general, aviation calculations involving POH values and used airplanes do not require this level of precision or accuracy.

If you are at an airplane, Pressure Altitude can be determined by setting 29.92 in the Kohlsman window and reading the altitude from the altimeter.

Many people calculate Pressure Altitude using the rule of thumb that 1″ Hg change equals 1000′ of altitude change. This rule of thumb is accurate enough for most aviation calculations, as long as you know its limitations. The rule assumes a linear change in pressure with altitude. This assumption is not correct but the answer doesn’t stray far from the truth when the values being calculated are below 10,000′ MSL. The rule, while easy to use, also has a minor inaccuracy as such that 1″ Hg change is not exactly 1000′ of altitude change but this issue should produce less than 100 feet of error per inch of change.

Density Altitude calculations have many of the same issues. In aviation, we use Pressure Altitude and temperature to calculate Density Altitude. Yet, in reality, humidity also has an impact on Density Altitude since water molecules in gaseous form are lighter than the typical molecules in the atmosphere. The more gaseous water (higher humidity) found in the atmosphere, the less dense the air and thus the higher the Density Altitude.

Why do we ignore humidity in common aviation calculations of Density Altitude? Apparently, it was decided at some time in the past that it doesn’t make that big of difference with regard to the performance of the airplane for practical purposes.

Performance Calculations

This brings us back to why we compute Pressure Altitude and Density Altitude in the first place. We want to know how the airplane is going to perform on a given day.

FAA test questions would have you believe that you should calculate your performance to the nearest foot. As most experienced pilots will tell you, this is not grounded in reality. POH performance numbers were developed with a brand new airplane being flown by a test pilot. Do you want to bet your life on a calculation with no error margin in your 5 (or 25) year old airplane being flown by a newly minted Private pilot?

The truth is, you need a safety factor.

One way to build in a safety factor and ease your need to calculate performance to the nearest tenth of a foot is to always round the value. Ignore the rounding rules that you learned in school and round to the next safest value. For example, if your Density Altitude calculation tells you that the Density Altitude for the day will be 3213.65 feet, use 3300 feet or better yet 4000 feet when you go to your POH to calculate your takeoff and landing performance.

You may notice some minor difference in the output for Pressure and Density Altitude when you compare various charts and models of E6Bs. This variation is likely due to the method that the manufacturer selected to compute these values. These differences are generally not significant for practical purposes and should not be a concern.

For the less than practical FAA tests, these differences may mean that you won’t get the exact answer as the FAA. Just use the closest answer and you should be fine. Don’t become overly concerned about this minutia; there are other minutiae on the tests that should have your attention.

In the real world, you are better off rounding up to the next safest value. This does away with things like interpolation on tabular data. It is also a simpler and safer practice.

Keep it simple and stay safe!

Half Sized Blog Element (Single Author Style)

Half Sized Blog Element (Multi Author Style)

Are you grading yourself as a pilot?

Performance on FAA Tests and in the Real World – Part 1

Are you grading yourself as a pilot?

Performance on FAA Tests and in the Real World – Part 1

Full Sized Blog Element (Big Preview Pic)

Are you grading yourself as a pilot?

Performance on FAA Tests and in the Real World – Part 1

Pressure and Density Altitude on FAA Tests and in the Real World

Variation in Pressure and Density Altitude Calculations

Performance Calculations

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