Save it!
The date that is. On July 12 at 3 PM Eastern. I will be presenting, "Getting Together Uneventfully." This is the same content that presented in June. If you missed the June event, please consider attending this Avemco sponsored webinar. See more details plus registration links on the Vectors for Safety" Events Page. Still unable to attend? There is a free online course available with the same content and also valid for Wings credit, as well as a video presentation with no Wings credit. Check these out here.
Applaud it!
An aviation accomplishment that is. A few months ago, I indulged myself by posting a personal note about my granddaughter Sara's first solo. I will now indulge myself an update to that posting. Sara has earned her Private Pilot Certificate and is now enrolled full-time at a major flight school. The 4th generation of Bensons to fly airplanes is well on her way! I am proud of all five of my grandchildren, but to have one beginning a career in aviation is special to me. Blue skies and tailwinds Sara!
Check it and lock it!
Baggage door latches that is. In July of last year, a Mooney M20K was substantially damaged during a rejected takeoff in Rhode Island. The pilot reported that he had latched and verified the baggage door prior to engine start. As he reached rotation speed on the takeoff, the door became unlatched and opened wide. His concern for his two dogs in the rear seat drove his decision to reject the takeoff. There was insufficient distance to stop and the airplane travelled beyond the runway, went down an embankment, and through a chain link fence. Fortunately, neither he, his passenger, nor the dogs received any injuries. The pilot's recommendation was to always lock baggage doors with the key as well as to ensure that they are latched. I firmly agree with the pilot. When the weight of the airplane shifts from the wheels to the wings, the fuselage often flexes allowing latches to slip. The key lock is an added step to securing the latch. Click here to download the accident report and here to download the Pilot-Operator Report.
Consider it!
Human error is at the root of most general aviation accidents. My Human Factors Ground School online course, valid for all three Wings credits at the basic level, is being offered for a limited time for $50 off. Click here for complete info and to enroll at the discount price.
Read it!
I have reduced the prices for all my publications to encourage summer reading! Scroll to the bottom of the blog or click here to visit my Author Page on Amazon.
What the Airplane Thinks
We all know that an airplane is an object, a collection of components that when assembled correctly can fly. As such, it cannot think. My brain knows that but, on occasion, after a hard landing, I have quietly wondered if the airplane thinks less of me. Okay, I plead guilty so several counts of personification of an inanimate object.
I also plead guilty to telling hundreds of students over the years that the airplane thinks. I have said that density altitude is the altitude at which the airplane thinks it is flying. That can be a segue into a quick review of density altitude which is highly appropriate for July.
Density altitude is a primary determiner of aircraft performance. As density altitude increases, aircraft performance decreases. All pilots already know that but sometimes fail to apply that knowledge and bend some metal or worse. Performance data provided by the aircraft manufacturer is typically for standard conditions at sea level which is defined as 59 degrees F. (15 degrees C.) and 29.92 in./Hg (1013.2 millibars). Performance can vary significantly from the published performance data as density altitude increases above standard.
Try to picture this. You are making a takeoff from a runway that has a length about the same as your home airport, but the airport elevation is about 500 feet higher and it is a warmer day than you are accustomed to. The airplane seems to be a bit sluggish as you begin the takeoff roll but it is gaining airspeed and the engine instruments all look good. The end of the runway is approaching but you are almost to rotation speed. As the airspeed indicator reaches the magic number, you rotate with about 50 feet of runway remaining. Just as you feel the relief of getting airborne with some runway unused, you notice the trees on the upsloping terrain ahead. The laws of physics have been challenged and have won. There is no way to climb over the trees, and a turn at such a low airspeed and high angle of attack invites a stall. You are going to crash. Let’s make sure that you are not that pilot.
High, hot, and humid are the factors driving density altitude. The higher the airport elevation, the hotter the air, and the moister the air, the higher the density altitude. We have some tools to help us calculate density altitude, but these tools typically ignore the amount of moisture in the air. According to an FAA publication, “At 96 degrees F., the water vapor content of the air can be 8 times as it is at 42 degrees F. High density altitude and high humidity do not always go hand in hand. If high humidity does exist, however, it is wise to add 10 percent to your computed takeoff distance and anticipate a reduced climb rate.”
The surface below the airplane while operating at a low altitude, such as immediately after takeoff, can also influence the humidity. This might have been a factor in a recent accident, described below. The pilot reported that his takeoff path took him over a corn field. He stated that at the current growth stage of the corn, the transpiration process likely added 15% to 30% to the relative humidity.
Just for review, higher density altitude results in increased takeoff distance, reduced climb rate, increased TAS (but the same IAS) on approach and landing, and increased landing roll distance. We must also remember that the normally aspirated engine should typically be leaned when operating at less than 75% power at density altitudes above 5,000 feet, regardless of the indicated altitude. Also, airplanes without turbochargers may need to be leaned for takeoff in high density altitude conditions.
Many pilots now use aps or software to calculate their aircraft performance and/or the density altitude. For the old school crowd, the old standby, the Koch Chart still works.
Koch Chart (Graphic Source: FAA)
Plug in a few examples on the Koch chart and it is obvious that density altitude is a huge player in the performance of our airplane. Accidents caused by pilots failing to adequately consider density altitude are very common. A common practice seems to be considering only takeoff distance and ignoring the need to clear obstacles and terrain on climb out.
The sticking point on the Koch Chart is the need-to-know pressure altitude. Just as a quick review, density altitude is pressure altitude corrected for non-standard temperature. It is important to use the actual temperature of the air surrounding the airplane. For example, the reported airport temperature is not measured directly over the runway. Hot sun on a dark surface can cause the air immediately above the runway to be considerably warmer than the reported temperature. Keep in mind the temperature used to calculate the takeoff performance and then just before takeoff, glance at the outside air temperature gauge. If it is showing much warmer than the temperature used in the calculations, the takeoff will require more distance than calculated. How much more? Good question. Of course, we could taxi back in and redo our calculations, but in the real world that is probably not going to happen. I am a firm believer in adding a minimum of 50% more to the calculated ground roll as a safety margin. If that has been already factored in, it will cover a few degrees variation. If the temperature difference is substantial, it is prudent to recalculate.
The easy way to determine pressure altitude, if an airplane is available, is to set the altimeter to 29.92 and simply read the altitude. If the airplane is not readily available, old-fashioned math works. The process is easy. Take the altimeter setting at the airport to be used and take the difference between it and 29.92. Since pressure changes by 1 inch of mercury per 1,000 feet, multiply the difference by 1000 to find the difference between the airport elevation and standard pressure. Now, if the airport altimeter setting was less than 29.92, add that to the airport elevation to determine pressure altitude. Likewise, if the airport altimeter setting was greater than 29.92, subtract the product from the airport elevation.
For example, if the airport elevation is 2,000 feet MSL and the altimeter setting is 29.32, we subtract 29.32 from 29.92 and get 0.60. We multiply 0.60 times 1000 and get 600. Since the airport altimeter setting was lower than 29.92, we add 600 feet to the airport elevation of 2,000 feet and get 2,600 feet for our pressure altitude.
And we must also allow a generous margin of safety. The performance data provided by the manufacturer was determined by a new airplane with a new engine, a new propeller, and flown by company test pilot. The data was perhaps a tiny bit overly optimistic when the airplane was new but might not adequately represent the airplane today with a few minor dents in the leading edges well hidden by the thin layer of bugs, and a couple of minor knicks in the prop. And oh yes, more than a few hours on the engine.
For taking off, the runway surface must be considered. Anything other than a dry, flat, paved, level runway will increase the distance needed to become airborne. The unknown is by how much it will be increased. The multitude of factors involved here make it impossible to assign a value. Remember that “probably” is not an acceptable word in our planning. If there is any doubt, do not attempt a takeoff. Two solutions though perhaps inconvenient, are to wait a few hours until the temperature cools off or to lighten the load.
So, let’s be sure to consider density altitude in our flying and to leave a healthy margin of safety. That’s what we mean by flying like your life depends on it.
Accidents discussed in this section are presented in the hope that pilots can learn from the misfortune of others and perhaps avoid an accident. It is easy to read an accident report and dismiss the cause as carelessness or as 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.
This crash happened in Nebraska in July 2020. The 247 hour private pilot, age 67, received minor injuries but the passenger was seriously injured. The Vans RV6 was substantially damaged. The NTSB accident report includes the following: "The pilot stated that this was his third passenger carrying flight of the day and he determined his takeoff weight was about 146 pounds below max gross weight. For the takeoff from the grass strip, he elected not to utilize flaps or the full length of the runway, leaving about 100-200 ft behind him. During the takeoff roll, the pilot had the sense that the roll was taking longer than normal, and he began to be concerned about powerlines at the end of the runway. When about 10-25 ft above the ground, he began a shallow bank turn to the right. Immediately after starting the turn, he flew over a corn field and experienced a loss of lift. The airplane then impacted the corn, resulting in substantial damage to the right wing and fuselage. The pilot reported no mechanical anomalies with the airplane that would have precluded normal operation. The pilot noted that he listened to the density altitude reported on the Automated Weather Observing System for a nearby airport but did not process the effects it would have on the accident flight. The density altitude was about 6,184 ft."
NTSB Photo
The NTSB Probable Cause finding states: "The pilot's inadequate preflight performance planning and his decision not to utilize all available runway during high density altitude operations which led to an inflight loss of control and subsequent collision with terrain."
NTSB Photo
We have all heard the old saying that a pilot begins flying with a full bucket of luck and an empty bucket of experience. The trick is to fill the bucket of experience before emptying the bucket of luck. The relatively low time pilot in this crash unfortunately emptied his bucket of luck before filling the bucket of experience. In his written report to the NTSB, he acknowledged that he should have used the full length of the runway and that he did not adequately consider the effect of the high density altitude. That brings to mind another old saying, "The most useless things in aviation are the runway behind you, the altitude above you, and the fuel left in the fuel truck."
The pilot included another good point in his statement. He recognized that the airplane performed differently when it exited ground effect. That is something for all pilots to keep in mind. If the airplane is struggling at the edge of its performance envelope, it will need to struggle more when it leaves ground effect. This is more noticeable in a low-wing airplane. If possible, staying in ground effect a bit longer and allowing the airplane to build additional airspeed before climbing out provides some additional safety margin in averting a stall.
Click here to download the accident report from the NTSB website.
Accidents discussed in this section are presented in the hope that pilots can learn from the misfortune of others and perhaps avoid an accident. It is easy to read an accident report and dismiss the cause as carelessness or as 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.
There were only two minor injuries but the Cessna 172 was destroyed in this crash that happened in Arizona. It occurred in Arizona in June 2017.
The NTSB accident report includes the following: "The pilot reported that, during an approach to runway 22, the airplane drifted to the right of the runway centerline. He initiated a go-around by turning off the carburetor heat, applying full throttle, decreasing the flaps from 30° to 20°, and pushing forward on the yoke to increase airspeed; the airplane then began to settle into ground effect. The pilot saw that the terrain began to rise, and he recalled that the noise abatement procedure called for a right turn to 270°, so he turned to the right before establishing a climb. The airplane descended into rising terrain, struck trees, and impacted the ground and became engulfed in flames. The postcrash fire destroyed the fuselage. The METAR reported that the wind was variable at 4 knots and that the temperature was 84°F. The field elevation was 5,504 ft, and the altimeter setting was 30.14 inches of mercury. The density altitude was 8,255 ft. Per the National Transportation Safety Board Pilot Aircraft Accident Report, the pilot reported that the accident could have been prevented by reviewing the airplane's performance data and atmospheric conditions, especially density altitude and its effect on performance per the manufacturer's Pilot's Operating Handbook. The pilot stated that he would place greater emphasis on performance planning as an essential activity during flight planning. The pilot reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation."
The 57-year-old private pilot reported having 92 hours total flight time, all in a Cessna 172.
NTSB Photo (courtesy of pilot)
The NTSB probable cause finding states: "The pilot's inadequate preflight planning that did not account for high-density altitude conditions and his subsequent attempted go-around in conditions that prevented the airplane from attaining a positive climb rate and resulted in its subsequent descent and impact with rising terrain."
An important lesson here is that density altitude applies to all aspects of flight, not just takeoff and climb. Had this airplane not drifted to the side of the runway, the pilot would most likely have made a successful landing. The go-around was essentially an unplanned takeoff but with a running start. The laws of physics are always at work.
Click here to download the accident report from the NTSB website.
Accidents discussed in this section are presented in the hope that pilots can learn from the misfortune of others and perhaps avoid an accident. It is easy to read an accident report and dismiss the cause as carelessness or as 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.
This accident supports our statement in the previous accident analysis that the laws of physics are always at work and they do not care how much ink is on the pilot certificate or in the logbook. The accident resulted in the destruction of an Aeronca 11AC. It happened in June 2017 in Michigan. The student pilot received only minor injuries and the 8,500 hour commercial pilot/flight instructor was not injured.
The NTSB accident report includes the following: "The flight instructor reported that, during the takeoff climb from a grass runway with the student pilot flying, about 25 feet above ground the "climb rate became stagnant." He added that he instructed the student to "lower the nose slightly," but after "several seconds the airplane did not resume a normal climb rate." The flight instructor took the flight controls and noticed that they were "sluggish" and it felt as if the airplane was caught in "wind swirls" and downdrafts. Subsequently, the flight instructor made a "small left turn" toward a small gap in the tree line ahead and the airplane impacted a heavily wooded/treed area."
The NTSB accident report also includes the following: "According to the flight instructor, the airplane departed "loaded at gross weight." The student pilot reported that the flight instructor did not discuss weight and balance with him before flight. During postaccident interviews with the National Transportation Safety Board investigator-in-charge, the student and flight instructor each reported their personal weight and a total of 10 gallons of fuel on board at takeoff. Based upon the information provided, the takeoff weight was 1,389 pounds, which was 139 pounds over the maximum gross weight (1,250 pounds) published in the airplane Pilot's Operating Handbook. The airplane's center of gravity for takeoff was within limits at 18.65 (12.4 to 22.0)."
The NTSB Probable Cause finding states, "The flight instructor's inadequate preflight planning, which resulted in a takeoff over maximum gross weight from a turf runway in high-density altitude conditions and the airplane's inability to attain a climb rate and subsequent collision with trees."
According to the NTSB calculations, the airplane was loaded about 10% over it allowable weight. Flying with more weight than allowed by the manufacturer's documentation is never a good idea. But flying 10% over the allowable weight in a high density altitude environment is really asking for trouble. Perhaps some complacency was at work here along with the laws of physics.
Click here to download the accident report from the NTSB website.
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