1. The Nine Deadly Sins Presented by KVGT FAASTeam
Sign Log In Sheet for Wings Credit
Stephen Ruks ATP, CFII

2. The Nine Deadly Sins References
Pilots Handbook of Aeronautical Knowledge Ch. 7 & 10
Your AFM or POH
AC 00-6A Aviation Wx
AC 61-84B Role of Preflight Preparation
FAA-P Density Altitude Brochure
FAA Aviation News
May-June 2004

3. The Nine Deadly Sins
What is one of the best things you can do to avoid being a sinner?
Enroll in the WINGS program!
FAA Safety - FAASTeam and Wings

4. The Nine Deadly Sins Introduction
Misunderstandings or lack of knowledge about our atmosphere and how it affects aircraft performance is one of the leading causes of fatal aviation accidents.
This seminar will remind you of some of the things you already know and maybe show you a few things you didn’t know.

5. The Nine Deadly Sins Altitude Types
How many altitude definitions are there?
Indicated altitude
True altitude
Absolute altitude
Pressure altitude
Density altitude
Read on your altimeter
Height above MSL
Height above ground level
Indicated altitude set at 29.92
PA corrected for non-standard temperature and humidity
1. Indicated altitude—read directly from the altimeter (uncorrected) when it is set to the current altimeter setting.
2. True altitude—the vertical distance of the aircraft above sea level—the actual altitude. It is often expressed as feet above mean sea level (MSL). Airport, terrain, 7-7 and obstacle elevations on aeronautical charts are true altitudes.
3. Absolute altitude—the vertical distance of an aircraft above the terrain, or above ground level (AGL).
4. Pressure altitude—the altitude indicated when the altimeter setting window (barometric scale) is adjusted to "Hg. This is the altitude above the standard datum plane, which is a theoretical plane where air pressure (corrected to 15 °C) equals 29.92" Hg. Pressure altitude is used to compute density altitude, true altitude, true airspeed (TAS), and other performance data.
5. Density altitude—pressure altitude corrected for variations from standard temperature. When conditions are standard, pressure altitude and density altitude are the same. If the temperature is above standard, the density altitude is higher than pressure altitude. If the temperature is below standard, the density altitude is lower than pressure altitude. This is an important altitude because it is directly related to the aircraft’s performance.

6. The Nine Deadly Sins Pressure
How do we describe atmospheric pressure, what is it, and how does it affect us?
More importantly, how does it affect our airplanes?

7. The Nine Deadly Sins Pressure What causes pressure variations?
Altitude
Pressure decreases approximately one inch of mercury per 1000 feet increase in altitude.
Temperature
Temperature is the biggest factor affecting density altitude.
Temperature changes ≈ 2ºC/1000ft

8. The Nine Deadly Sins Pressure Gradient
Given the same change in pressure, the rate of change of pressure is greater in cold air than in warm air.

9. The Nine Deadly Sins
Effect of non-standard temperature

10. The Nine Deadly Sins
Typical GA Pitot System

11. The Nine Deadly Sins
Typical Altimeter

12. The Nine Deadly Sins Altimeter Setting Standard Atmosphere:
29.92 inHg or
hPa (or mb)
At sea 59º F (or 15º C)
One inch of mercury = 1000 feet
One hectoPascal = 100 millibars
1 inHg = hPa

13. DA= Tsl γ 1 − 𝑃/𝑃𝑠𝑙 𝑇/𝑇𝑠𝑙 𝜞𝑹 𝒈𝑴−𝜞𝑹
The Nine Deadly Sins
Density Altitude
How do we calculate Density Altitude?
DA= Tsl γ 1 − 𝑃/𝑃𝑠𝑙 𝑇/𝑇𝑠𝑙 𝜞𝑹 𝒈𝑴−𝜞𝑹

14. The Nine Deadly Sins Density Altitude
Three important factors contribute to
high density altitude
Altitude
Temperature
Humidity
Reduced air density equates to
decreased performance

15. The Nine Deadly Sins Density Altitude
Warmer air will hold more water vapor than cooler air which affects engine performance more than aerodynamic performance.
With high humidity, expect longer take-off rolls and lower climb rates. Add 10% to take-off distance.

16. The Nine Deadly Sins The Nine Deadly Sins (and their unforgiveness)
Using sea level VSPEEDS
Using gross weight VSPEEDS
Ignoring effect on TAS
Ignoring effects in mountainous terrain
Ignoring effects on landing speed and distance
Ignoring climb gradient
Ignoring runway environment
Using incorrect flap settings
Combining soft-field and obstacle techniques

17. The Nine Deadly Sins 1.
Using Sea Level
VSPEEDS
Best Climb Chart

18. The Nine Deadly Sins 1. Using Sea Level VSPEEDS
High density altitude affects take-off & landing distance
Always follow manufacturer’s recommendation.

19. The Nine Deadly Sins 2. Using Gross Weight VSPEEDS 𝑉𝑦𝑐𝑢𝑟𝑟𝑒𝑛𝑡
=𝑉𝑦𝐺1 2 𝑊𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑊𝑔𝑟𝑜𝑠𝑠
Climb performance decreases with increase in gross weight

20. The Nine Deadly Sins 3. Ignoring Effect on TAS IAS = 150 PA = 8000 Vy
Temp = 95ºF
TAS = 180
DA = 12,000 Vy
TAS Vx
TAS

21. The Nine Deadly Sins 3. Ignoring Effect on TAS
IAS = 150
PA = 8000
Temp = 95ºF
TAS = 180
DA = 12,000
Turn diameters increase.
Bank angle = 23=SRT
((v² / (11.26 x Tan Φ)) x 2) / 6076
((150² / (11.26 x )) x 2 ) / 6076 = 1.55NM
@ 180 TAS = 2.23NM
Turn diameter increased by 50%

22. The Nine Deadly Sins 4. Ignoring Effects In Mountainous Terrain
TAS increase causes turn diameter to increase

23. The Nine Deadly Sins 4. L - D Chart
Bank Angle Load Factor %Increase in Induced Drag
Stall speed (VS1) increases a whopping 41%

24. The Nine Deadly Sins 5. Ignoring Effects on Landing Speed and Distance
PA=4000’, 25ºC, No wind – 1200ft
PA=6000’, 38ºC, 10kt Tail – 2200ft
PA=6000’, 38ºC, 10kt Tail – 3400ft w/ obstacle

25. The Nine Deadly Sins 6. Ignoring Landing Distance
8000’ elevation, 2500’ long, downslope, tailwind, cliff

26. The Nine Deadly Sins 6. Ignoring Climb Gradient
Climb gradients are in Feet/Mile
not Feet/Minute (as read on VSI)
Use TAS (or GS) not IAS to calculate climb gradient

27. The Nine Deadly Sins 6.
Ignoring Climb Gradient

28. The Nine Deadly Sins 6.
Ignoring Climb Gradient

29. The Nine Deadly Sins 7. Ignoring Runway Environment A36 Takeoff
OAT = 97F, Field Elev =1293’ Altimeter 29.89”
Density Altitude = 4125’, Rwy ’ paved
1996 A36, Turbonormalized IO 550,
GTOW = 4095, CG = 86.15”

30. The Nine Deadly Sins 8. Using Incorrect Flap Settings
In the A36 incident, use of flaps may have made the situation even worse!
Use of the recommended flap setting works just fine when operating at near sea level altitudes but with non-turbocharged engines, there comes a density altitude above which the use of takeoff flaps actually increases ground roll.

31. The Nine Deadly Sins 9. Combining Soft-Field & Obstacle Techniques
Normally flaps only used on soft field takeoff but when used for obstacle clearance, the increase in drag drastically hinders climb performance.
Always follow manufacturer’s recommendation.

32. The Nine Deadly Sins Summary
Beware, better yet, be knowledgeable, of the Nine Deadly Sins of Density Altitude
Remember the effect of DA on TAS and
the TAS effect on airplane performance
Engine performance degrades with altitude
and humidity!
Always use POH or AFM recommendations

33. The Nine Deadly Sins
Any Questions?

34. The Nine Deadly Sins
That’s all folks!

35. Door Prize! The Nine Deadly Sins
Remember to sign the Log-In Sheet for credit.
Stephen Ruks ATP, CFII, BPPP

36. The Nine Deadly Sins
Remember to sign the Log-In Sheet for credit.

37. The Nine Deadly Sins
The end