Standard Day (ISA ± 0°C) - - AIRPLANE (Single Engine Land)

Your Takeoff Safety Connection! ®

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Ratio ("true-zero") Data - - STANDARD DAY (temperature 15°C/59°F & sea level pressure altitude).

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Cessna™ SkyCatcher

Cedar Key (FL) CDK - - George T. Lewis Airport

Temperature 14.93°C/58.87°F

Field Elevation - - Seven Feet

Pressure Altitude (PA) - - Seven Feet (altimeter set 29.92 in.Hg or 1013.25 hPa [millibars])

Density Altitude (DA) - - "0" Feet (a seasonal environmental condition!)

Runway Length - - 2,355 FEET

Schemata language is accurate, concise & unambiguous. Here, a ratio-level is evident because a "true-zero" resides at the point of x-axis & y-axis intersection. Why is this important? The ratio level of measurement will always include nominal named categories. The ratio level reporter will always allow the observer to rate or rank the data. But for even quantitative intervals, it is always capable of mathematical/statistical expression (interval data). In furtherance, the ratio level will accommodate intense scrutiny because a line function is able to correlate an elusive causation with an explainable effect.

The Koch Chart below reflects the FAA's ongoing concern for high density altitude takeoff safety. This site provides ample on-line instruction in applying & correlating a high density altitude with takeoff distance & climb rate.

A density altitude of sea level yields a takeoff distance over a 50' obstacle of 1,250 feet (381 meters) because 770 (234.7 m) + 480 (146.3 m) = 1,250 feet (381 m). We need not contemplate the use of the Koch chart for this standard day sea level condition because we achieve nominal prototypical performance under these stated conditions. The CDK runway would appear to be quite adequate. But for 1,250 ft required to clear a 50' (15.2 m) obstacle & a landing distance over a 50' (15.2 m) obstacle of 1,040 ft (317 m); our summation reveals something troubling. 1,250 (381 m) + 1,040 (317 m) = 2,290 feet (698 m). If an engine failure were to occur at 50', there is very little margin for A SAFE LANDING! In furtherance, this also assumes timely identification of the emergency along with landing flaps set without delay!

Recall the runway length is only 2,355 feet (0.718 km). Here, a short runway under standard day conditions at maximum gross weight and an engine abnormality could result in serious consequences. A standard day sea level density altitude yields a rate of climb of 890 ft/min (271 meters/minute). We do not need to contemplate the use of the Koch chart just yet! Since the ground roll is 770 feet (234.7 m), we need only subtract this from 1,250 ft (381 m) to obtain a figure essential for determining climb gradient! If 1,250 - 770 = 480 feet, & the height gain is 50', the climb gradient can be determined. But for 50' divided by 480 = 0.104 (15.2 m divided by 146.3 m = 0.104) we have a climb gradient of 10.4%. Notice 480 x 0.104 = 50' & 146.3 m x 0.104 = 15.2 m. So let's analyze the takeoff from Cedar Key (CDK) Lewis Airport:

Here, 770 ft (ground roll) + 480 feet (initial climb distance) = 1,250 ft. The runway length at CDK is 2,355 ft - 1,250 ft = Distance to end of runway = 1,105 feet (336.8 m).

This means, 1,105 ft x 0.104 = 114.9 feet (height gain) altitude at the runway end. This means 336.8 m x 0.104 = 35 meters (height gain) altitude at the end of the runway! Climb gradient is poorly understood & rarely contemplated by the general aviation pilot. Contrast this with Part 121 airline operations, climb gradient is a rule of law! If you are a general aviation pilot, your primary concern is to achieve a positive rate of climb upon lifting off at a safe rotate speed.

Gusts, turbulence & wind shear coupled with a high density altitude are elements that are often associated with untenable airplane performance that not even the best pilot skill can overcome. A recent NTSB investigation revealing probable cause is available by way of the NTSB site. Here, you have an interpretation of probable cause with a data array that is graphic & interpreted that is preceeded by a factual condenced outline. Through your subscription, you should read the outline to see how many performance issues you can identify. You will learn something about errors of omission on the part of this pilot-in-command.

Now you will be making a hypothetical journey across a spectrum of density altitudes & performance capabilities. Your login privilege ensures that this tutorial serves as consolidation, revision & system safety recurrency. Knowing this subject, & knowing it well contributes to judgment & decision making.

If the Takeoff Ground Roll is Predicted to be 770 FT (235 m), then a kinematic solution fixes the time at 20.882 seconds.

Here, 770 FT ground roll + 480 FT additional, yields 1,250 feet total. Even under sea level & standard day conditions, the climb gradient 0.108 or 10.8%. The aircraft here are prototypical where all performance claims are biased in favor of precise pilot technique for standard day conditions.

You may analyze/apply the interpreted data presented on the following pages. Technically speaking, the SkyCatcher's maximum takeoff weight is 1,320 lbs. This yields an inertial mass to be accelerated the 770 feet (235 m) is 1,320 lbs. ÷ 32.2 ft/sec² (accelerating force due to earth gravity) = 40.994 slugs.

Newton's second law is controlling where force = mass x acceleration. But for this equation, (40.994 slugs x 4.334 ft/sec² = 177.667 Lbs [598.3 kg x 1.321 m/sec² = 790 Newtons]) Effective Thrust available for accelerating this airplane "mass" to takeoff velocity. Metric units are for our friends in Canada, Australia, New Zealand & South Africa (& most of the world using the metric system).

A total of 1,250 feet horizontal displacement is required to clear a 50 FT obstacle. The "density altitude" pilot will use this data to acknowledge a positive rate of climb is attainable. This revelation is used to make predictions with respect to the next phase of flight. That next phase is the all important enroute climb.

In furtherance, effective thrust is the amount of force to overcome runway friction, aerodynamic drag & t.o. mass. Upon liftoff at 770 ft (235 m), excess power where Lift > Drag results in an acceptable climb profile where Lift > Weight (1,320 lbs [598.7 kg]). The climb profile is seriously degraded as we contemplate higher density altitudes where lower air densities reside. Lower air densities are found where pressure altitudes and/or temperatures are above ISA Standard. Here, time is of the essence. The longer the time interval, the greater the takeoff distance & the lower the rate of climb. But for standard day conditions, aircraft performance is adequate in CDK. Is standard day an exception to what normally prevails in the sunshine state? If you want data, it can be found in every corner on the internet. If you want interpreted data, this and other Runwaydata.com websites confront this issue head on.

Density altitude is pressure altitude corrected for a non standard temperature. True airspeed is corrected for calibration errors as well as non-standard temperature & pressure. Since "ratio" level graphics are sensitive to time; distance, velocity & acceleration rates are explainable. The pilot-in-command is able to predict the effect of the environmental situation with a high degree of control (go/or no-go).
Environmental concerns include speed [takeoff velocity (knots true airspeed)] & ground roll distance as a function of acceleration rate because runway lengths are often limited. Since some high density altitude airports have rising terrain, trees, obstacles & buildings in close proximity; extra planning & vigilance are essential pilot duties.

Anytime temperature is above standard, the density altitude increases dramatically. Here, a pilot's omission can be serious.

The applicable rule is 14 CFR Part 91.103 (b.)(2.) Preflight Action requiring the use of other reliable information that contemplates the effect of temperature, pressure altitude & takeoff weight (including wind & slope).

Here, the issue is a non-standard temperature that attaches to an existing pressure altitude.

Line graphs fix an applicable density altitude. Here, we identify causation. If we attach the above regulation as an applicable rule to the stated issue, we have begun to analyze.

Interval (numerical/quantitative) graphs reveal the effect of deviation from standard day temperature & pressure. Here, the pilot performs the most critical step where a quantitative analysis/application reveals a probable/likely outcome.

Flying safety is reliant on the pilot-in-command (PIC) concluding either way toward a go (or no-go) decision. The PIC may elect not to go if any adverse meteorological condition (or technical issue) still exists or arises.

Environmental awareness is found where the PIC exercises professional decision-making & judgment. His/her decision can go either way based on a careful analysis.

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