Mountain Flying

1. Mountain Flying AwarenessRisk ManagementSafety Practices by Kurt S. Kleiner - CFI

2. According to Aviation Space Environment Medicine, 232 airplanes crashed within 50 nautical miles of Aspen, CO, between 1964 and 1987. A total of 202 people died and 69 were seriously injured. This points out the need for better training in mountain flying.

3. Hazard Categories Aircraft Performance • Effects of Density Altitude • Aerodynamics of Maneuvering Flight Weather/Environmental • Convective and Orographic lifting forces • Micrometeorology: Terrain and Wind Interaction • Winds Aloft and Mountain Wave Unforgiving Terrain • Crossing Ridges • Operating in Canyons • Take-offs and Landings at Remote Sites Human Factors • Aeromedical Factors • Aeronautical Decision Making (ADM) • Training and Proficiency • Contingency Planning and Survival Strategies

4. Density Altitude • Defined as “pressure altitude corrected for non-standard temperature.” • High relative humidity also affects DA, but to a very minimal extent. It is rarely ever factored into calculations. • In terms of aircraft performance, another way to look at DA is: “Density Altitude is the altitude the aircraft thinks it is at, and performs accordingly.” • Questions to be answered: • What is “Pressure Altitude?” • What is “standard” vs. “nonstandard” temperature?” • How does Density Altitude affect aircraft performance and mountain flying safety?

5. What is “Pressure Altitude?” Pressure altitude is the altitude displayed on an altimeter when it is set to an agreed baseline pressure setting. The International Civil Aviation Organization (ICAO) utilizes the barometric pressure setting of 29.92 inches of mercury (Hg) as equivalent to the air pressure at mean sea level (MSL) in the International Standard Atmosphere. 29.92 is STANDARD pressure.

6. When barometric pressure is above or below the “standard” 29.92 inches of Hg, Pressure Altitude (PA) will be lower or higher than field elevation. Pilots acquire the current barometric pressure from any one of several official FAA-approved sources of weather information. This conversion chart may be used to assist in calculating Pressure Altitude on any given day. ADD 28.3 1535 feet 28.4 1435 28.5 1340 28.6 1245 28.7 1150 28.8 1050 28.9 955 29.0 865 29.1 770 29.2 675 29.3 580 29.4 485 29.5 390 29.6 300 29.7 205 29.8 110 29.9 20 SUBTRACT 29.92 0 feet 30.0 - 75 30.1 - 165 30.2 - 255 30.3 - 350 30.4 - 440 30.5 - 530 30.6 - 620 30.7 - 710 30.8 - 805 30.9 - 895 31.0 - 965 Note: HIGH atmospheric pressure is better for aircraft performance than LOW pressure.

7. What is “Standard” vs. “Non-Standard” temperature? The International Civil Aviation Organization (ICAO) baseline for all aircraft performance data is a “Standard Temperature” of 15 deg. Celcius (or 59 deg. F) AT SEA LEVEL, and a mean standard atmospheric lapse rate of 2 deg. C (or 3.5 deg. F) per 1,000 ft. of altitude (up to 36,000 ft.) The following chart establishes the STANDARD TEMPERATURE for each 1,000 ft. of altitude.

8. Standard Temperature at MSL Altitudes AltitudeDeg. (C)Deg. (F) 14,000 -13 10 13,000 -11 13.5 12,000 -9 17 11,000 -7 20.5 10,000 -5 24 9,000 -3 27.5 8,000 -1 31 7,000 1 34.5 6,000 3 38 5,000 5 41.5 4,000 7 45 3,000 9 48.5 2,000 11 52 1,000 13 55.5 Sea level 15 59 To determine DENSITY ALTITUDE, add 117.4 ft. to the Pressure Altitude for each degree Celcius above standard temp.

9. Airport elevation: 7,420 ft.Solve for Density Altitude Altimeter/Barometer: 29.3” Temp. 80 deg. F or 27 C (Std. temp. at 7,500 = 0 deg. C) 28.5 1340 28.6 1245 28.7 1150 28.8 1050 28.9 955 29.0 865 29.1 770 29.2 675 29.3580 29.4 485 29.5 390 29.6 300 29.7 205 29.8 110 29.9 20 29.92 0 feet 30.0 - 75 30.1 - 165 30.2 - 255 30.3 - 350 30.4 - 440 Airport Elevation (MSL) 7,420 Correct for non-std. pressure + 580 Pressure Altitude (PA) = 8,000’ Current temp. is 27 deg. warmer than std. temp. Calculate for non-std. Temp. 27 X 117.4 ft. = 3,170 ft. PA 8,000’ Add temp. factor to PA: + 3,170 DENSITY ALTITUDE = 11,170’

10. The non-standard temperature conversion is usually calculated via the Density Altitude chart shown below. A copy of this chart can be found in Chapter 10 of the FAA “Pilot’s Handbook of Aeronautical Knowledge” available at www.faa.gov and in several Aviation and Weather publications.

11. Another example: PA = 5,000 ft. Temp.= 40 C DA = 8,800 ft.

12. How does Density Altitude adversely affect aircraft performance? Increases the runway distance required for take off and landing, increases ground speed. Decreases allowable payload, service ceiling, climb performance, and the ability to out-climb terrain and downdrafts. Reduces effectiveness of control surfaces, engine, and propeller. Normally aspirated (non-turbine) engine horsepower output decreases by 3% for each 1000 ft.

13. Know the limitations of your aircraft and how to use the POH performance charts! When the Density Altitude is 10,000 ft., this aircraft will not be able to out-climb any downdraft that exceeds 230 feet per minute. Downdrafts of 500 to 1,000 feet per minute (fpm) are common on the immediate lee side of mountains when the winds aloft exceed 25-30 knots, and areas of 2,000 fpm sink are common on the lee side during mountain wave.

14. “It just seemed to take forever to get off the ground….. I had to yank hard on the stick at the last second to make it over the row of tree tops directly in front of me. The last thing I remember was the sound of the stall warning horn just before we hit the ground.”Confession by an anonymous private pilot

15. Environmental Hazards and Operational Limitations

16. Operating aircraft in the mountain weather environment presents unique challenges to pilots. • Poor aircraft performance due to high Density Altitude • Strong areas of lift, sink, and turbulence • Rapidly-forming summer thunderstorms • Low cloud ceilings and “mountain obscuration”

17. Wind is the most dynamic element in mountain flying and has the most immediate effect on aircraft performance and safety of flight. • On a large scale, the direction and strength of wind is determined by the proximity of high and low pressure areas and the gradient of change between them. Expect high wind where the pressure gradient is high, as shown by isobars compressed close together on weather maps. • On the micro-scale, the speed and direction of wind flowing through canyons and up/over mountain slopes is largely determined by solar heating and the terrain itself. • Moving air demonstrates the same FLUID PROPERTIES as water flowing over and around rocks in a creek or river.

18. Favorable conditions and updrafts are found on the upwind side of a mountain due to orographic lifting. Downdrafts and turbulence may be encountered anywhere, but are found in abundance on the leeward side. When the wind speed exceeds 20-25 kts., avoid flying on the lee side unless well above the altitude of the ridge or mountain top. Expect an increase in wind speed (venturi effect) and possible change in direction where air is forced through a gap or constriction, such as a saddle, mountain pass, or in a canyon. When the wind is light, proceed cautiously.

20. Solar Heating: In the morning, the south and east sides of a canyon or mountain will receive direct sunlight that triggers thermal columns or bubbles of rising air if the airmass is unstable. In the afternoon, look for lift on the southwest facing slopes, especially where rock outcrops and areas without trees can absorb heat and serve as trigger points. Remember: What goes UP must come DOWN. Wherever there is favorable lift from a thermal, there is sinking air somewhere nearby. In the shear area where the rising air mixes with sink, expect turbulence and some noise from the stall horn.

21. Anatomy of a Thermal

22. If there is sufficient water vapor in the rising unstable air, cumulus clouds will form when the thermal has reached a height where the moisture visibly condenses. When the lapse rate is weak, or if there is a stable layer of air above, this can occur at an altitude below the highest terrain. Though some terrain can become obscured, you can expect only light turbulence.

23. The base of each fair-weather cumulus cloud marks the top of a thermal. Expect rising air beneath each cloud, sinking air between clouds and turbulent air at altitudes below cloud base.

24. Glider pilots say, “There’s no place like cloud base!” Thermal soaring doesn’t get any better than this.

25. Beware of rapid over-development that commonly occurs during afternoon mountain flights.

26. Tips for flying in mountain turbulence: Flying conditions are most favorable during early morning hours. Cooler temperatures (lower DA) improve aircraft performance. Strong thermals are not normally produced until late morning and then continue through the afternoon. Maintain an airspeed well above stall speed, but at or below the published maneuvering speed (Va) to avoid excessive loads on the airframe. Research and understand your aircraft performance limits. If you encounter a strong downdraft, maintain adequate altitude and clearance from terrain so that you can pitch down (sacrificing altitude for airspeed if necessary) to avoid a stall. Use only a shallow to moderate bank angle to immediately turn toward lower terrain.

27. Tips for flying in mountain turbulence (continued): Do not fly on the leeward side of a peak or ridge any lower than eye level with the highest terrain if the wind speed is more than 20-25 kts. to avoid the rotor. If the wind speed is higher, increase your margin of altitude. 5. Become a devoted student of mountain weather so you understand the cause of the turbulence, where and when to expect it, and how to manage the risk. Establish and adhere to personal limits that specify maximum winds and minimum AGL altitudes.

28. Mountain Wave This weather phenomena creates the strongest downdrafts and most extreme turbulence found in mountain flying, second only to severe thunderstorms.

29. Necessary Ingredients for Mountain Wave: Stable airmass (or inversion below 15,000 ft.) Wind striking a mountain range from a direction within a 30 degree angle of directly perpendicular. Wind speed of 25 kts. or greater striking the mountains with higher wind speeds above, and no change in direction. Orographic lifting forces air upslope. The stable atmosphere prevents further lifting and forces air to flow down the lee side where it cools and becomes denser than surrounding air. The air essentially “compresses and rebounds back” several times as it seeks equilibrium and weakens. When the wind is strong, multiple wave crests with intermittent bands of strong lift and sink extend downwind for hundreds of miles.

30. Bands of mountain wave extend downwind, eastward from the Sierra Nevada, makes the Owens Valley, CA a prime location for glider pilots seeking world altitude records of over 40,000 feet. Cross country distance records are set on thermal flights. Anatomy of Mountain Wave conditions

31. Mountain wave is not always visible if the air mass is dry. When there is sufficient water vapor in the atmosphere, Altocumulus Lenticularis or “Standing Lenticular” clouds will form downwind of the peaks, often in stacks.

32. Roll clouds and rotor clouds have the innocent appearance of small cumulus clouds that form beneath a lenticular cloud. Severe or extreme turbulence is found in or near the rotor area.

33. A “cap” cloud often enshrouds mountain summits during wave conditions. Note the “rotor cloud” that forms beneath the Lenticular cloud marking an area of severe turbulence for all aircraft. Many serious accidents have occurred when aircraft flew through the rotor during strong mountain wave conditions.

34. NTSB Accident Report: Mountain Wave incident • NTSB Identification: DCA93MA033. Probable Cause Approval Date: 5/10/1994Scheduled 14 CFR EVERGREEN INTERNATIONAL Aircraft: BOEING 747-121, #N473EVAccident occurred Wednesday, March 31, 1993 in ANCHORAGE, AKInjuries: 5 Uninjured. • SHORTLY AFTER TAKEOFF FROM ANCHORAGE, THE AIRPLANE FLEW INTO AN AREA OF SEVERE TURBULENCE, WHILE CLIMBING THROUGH AN ALTITUDE OF ABOUT 2000 FEET. THE NUMBER 2 ENGINE AND ENGINE PYLON SEPARATED FROM THE AIRPLANE.THE FLIGHTCREW DECLARED AN EMERGENCY AND THE FLIGHT RETURN TO ANCHORAGE, WHERE AN UNEVENTFUL LANDING WAS ACCOMPLISHED. THE INVESTIGATION REVEALED THAT A STRONG EASTERLY WIND INTERACTED WITH MOUNTAINS EAST OF ANCHORAGE, WHICH PRODUCED MOUNTAIN WAVE ACTIVITY. THE AIRCRAFT ENCOUNTERED SEVERE OR POSSIBLY EXTREME TURBULENCE. THERE WAS EVIDENCE THAT THIS RESULTED IN DYNAMIC MULTI-AXIS LATERAL LOADINGS THAT EXCEEDED THE ULTIMATE LATERAL LOAD-CARRYING CAPABILITY OF THE NUMBER 2 ENGINE PYLON, WHICH HAD ALREADY BEEN REDUCED BY THE PRESENCE OF A FATIGUE CRACK NEAR THE FORWARD END OF THE PYLON'S FORWARD FIREWALL WEB. • The NTSB determines the probable cause(s) of this accident as follows: • THE LATERAL SEPARATION OF THE NO. 2 ENGINE PYLON DUE TO AN ENCOUNTER WITH SEVERE OR POSSIBLY EXTREME TURBULENCE THAT RESULTED IN DYNAMIC MULTI-AXIS LATERAL LOADINGS THAT EXCEEDED THE ULTIMATE LATERAL LOAD-CARRYING CAPABILITY OF THE PYLON, WHICH WAS ALREADY REDUCED BY THE PRESENCE OF THE FATIGUE CRACK NEAR THE FORWARD END OF THE PYLON'S FORWARD FIREWALL WEB.

35. In addition to generating turbulence that is sufficient to significantly damage aircraft or lead to loss of aircraft control, the more prevailing danger to aircraft seems to be the effect on the climb rate of an aircraft. There are several catastrophic aircraft accidents on record in which the NTSB used the following language in their statement of probable cause: "The airplane collided with mountainous terrain after encountering turbulence and downdrafts associated with mountain wave conditions. It is probable that the maximum climb performance of the aircraft was not capable of overcoming the strong downdrafts in the area at the time.”

36. Recall this performance chart? You are the pilot of a light single engine aircraft that contains this chart in the POH. The temperature is only 20 deg. F at your altitude of 11,000 ft. and your GPS is indicating a 40 knot headwind. The best you can get from your engine is 300 fpm of climb when pitched for Vy at full power. Conditions are clear VFR, but Lenticular clouds are streaked across the sky above you. You wish to penetrate the lee side rotor of a 10,000 ft. peak just ahead along your route. What decision(s) will you make?

37. Tips for flying light aircraft near mountain wave: Avoid flight on the lee side of the peak whenever possible. If you cannot fly around the area of wave and you must cross through the lee side downdrafts, fly at an altitude well above eye level with the top of the peak. A good rule of thumb is to fly an altitude of at least one half the height of the peak (from its base to top) above the peak. For example, if the base of the peak is at 7,000 ft. and the summit is 11,000 ft., add 2,000 ft. to the summit altitude and fly over the lee side at no lower than 13,000 ft. for a safety margin.

38. Tips for flying light aircraft near mountain wave (continued): 2.Avoid flying through or near the rotor found directly beneath the Lenticular cloud where you might encounter severe to extreme turbulence and loss of aircraft control. Establish a personal maximum “winds aloft limit” (i.e. 30 or 40 kts.?) Don’t fly near wave if the wind speed is higher until you receive training, acquire more experience, and develop strategies for recognizing and avoiding rotors. 4. You may eventually learn to work the upwind side of the wave crest to maximize your altitude gain. Once you find the lift, turn into the wind, pitch for Vy or best L/D speed, and crab back and forth, right and left. Establish a “hovering” flight path like a seagull would, soaring above a sand dune in a strong sea breeze using ridge lift.

39. Canyon Flying Rule #1: Get instruction from a qualified flight instructor experienced in mountain and canyon flying before attempting to fly in canyons on your own. Rule #2: Always be in a position where you can descend and turn toward lower terrain at idle power. (Always have a “way out.”) Rule #3: Never fly up canyon toward rising terrain beyond the “point of no return” from which you cannot exercise Rule #2 above.

40. Tips for flying in canyons: In addition to flying by Rules #1, 2, and 3…… Always stay far to one side of the canyon (preferably the sunny side where thermals might provide lift) so you have room to turn around and escape if necessary. If you must fly IN a canyon, it is best to fly down-canyon so there is always descending terrain ahead. Avoid flying down the center where the most turbulent air is found. 3. Perform a high reconnaissance of the canyon before descending into it. Assess the wind speed and direction, locate areas of lift and sink, note hazards such as power lines, and determine the safest route in and out in case you need to escape.

41. Remaining far to one side of the canyon allows ample room to make a 180 degree, shallow-to-moderate banked turn to escape, if needed. Flying over the sunny south or southwest facing slopes usually offers the benefit of thermals and additional lift from rising air. There are exceptions to this general rule which you should know about.

42. When is the south or southwest facing slope of a canyon a place where you might not benefit from thermals? Overcast days and snow covered or heavily forested terrain are not prone to surface heating and thermal generation. If the atmospheric lapse rate is stable, or there is a temperature inversion, thermals are weak or not triggered. When a strong north wind is found at the top of a sunny south aspect, the air will probably spill over and create downdrafts and turbulence (rotors) on the south aspect, even on sunny, unstable days. Look for ridge lift above the north aspect. If there is a strong pressure gradient and a gravity wind (i.e. a Chinook) is blowing down the canyon, thermals triggered by surface heating will rarely stay intact or be useful for lift. Even when thermal columns develop above a south aspect, there are downdrafts and turbulence found on the edge of the column and in the air between the areas of lift.

43. Pilots recall downdraft, crash, and hike for help By MARGA LINCOLN - IR Staff Writer, Great Falls Tribune - 06/06/07 • Two pilots said a surprise downdraft led their single-engine • plane to crash in the Elkhorn Mountains late Sunday morning.Jon C. “J.C.” Kantorowicz, 58, of Great Falls said he was • practicing canyon flying with mountain flight instructor Sparky • Jim Imeson when a surprise downdraft pushed the plane down. • The practice was part of a training exercise during a mountain • flying safety training workshop this past weekend in Townsend. • The pilots were flying at approximately 300 feet,which left • little room to maneuver when the downdraft caught the • plane, Imeson said. Downdrafts are a natural cycle of the • air, Imeson said. However, so far that day, they had only • encountered updrafts. “The one spot where we did not need • a downdraft to be there, there was one,” Imeson said. “I was • trying to turn away from the hillside,” Kantorowicz said, but the aircraft stalled. “I tried to fly between the snags.” The dead trees were about 60 feet tall. When they touched down, the landing gear sheared off and the engine hit a rock, Kantorowicz said. He said the whole accident happened in a span of five seconds. Imeson, 62, a nationally renowned mountain flight instructor from Jackson, Wyo., said the plane went down at “11 a.m. (Sunday) on the dot.” Both pilots were able to get out of the Aviat Husky, on their own power, following the crash, before it completely burned.

44. Excerpt from NTSB report #LAX07-CA187 Winston, MT 6/3/07 …..They flew the first canyon at 300 feet agl, 70 mph, 20 degrees of flaps, along the south side of the canyon, and rode a few thermals. Identifying areas where thermal lift could be found was part of the instructional flight. He then crossed into another canyon that was full of burned terrain and dead fall trees. This canyon he flew at 300 to 350 feet agl, 60 to 65 mph, and full flaps. The pilot angled his plane towards a rock cliff expecting to pickup thermal lift from the warm rocks. He flew with the wing tip about 10 feet from the cliff. The climb stopped, the airspeed fell off, and the wing stalled. He turned left, applied full throttle, and lowered the nose of the airplane. The descent was rapid as he tried to direct the airplane between deadfall trees into a drainage gully. The airplane's descent continued and he tried to land the airplane as gently as he could. After the collision with the sloped terrain, both pilots egressed the airplane just before it was engulfed in flames. The pilot stated that the airplane and engine had no mechanical failures or malfunctions during the flight. The National Transportation Safety Board determines the probable cause(s) of this accident as follows. The pilot's failure to maintain an adequate airspeed while maneuvering at low altitude in a canyon that led to a stall. The pilot's decision to fly along the canyon wall at a low altitude and low energy state was a factor.

45. There is no specific reference in the NTSB Narrative Report about the aircraft’s exact bank angle at the moment it stalled. According to the manufacturer’s data, the Aviat Husky A1-B has a stall speed of 43 mph or 37 kts. (power on, wings level, flaps extended). As shown in the graph below, the wing will stall at a 20% higher speed (52 mph) when banked to 47 degrees. Stall speed increases by 40% (60 mph.) if banked to 60 degrees. _________________________________________ • The keys to safely flying out of downdrafts and turbulence are: • Airspeed well above stall • Altitude (terrain clearance) • Shallow/moderate bank angles • Factors that help include: • Adequate engine horsepower • Flight in favorable conditions: • Light winds, Low Density Alt., • Stable Lapse Rate, etc.

46. Crossing Ridges: When possible, approach ridges from the upwind side to benefit from the cushioning effect of the upslope wind. Approach the ridge with extra altitude (1,000 ft. AGL) at a 45 degree angle so you have adequate room to turn back toward lowering terrain if a downdraft is encountered. Once the ridge is crossed, turn toward lower terrain and maintain airspeed as you penetrate the downdrafts and turbulence on the lee side. If the terrain on the lee side is a flat plateau, maintain extra altitude and airspeed. You won’t have as much room to escape down-slope.

47. Cross ridges with an escape plan in mind. If the wind speed is greater than 25-30, give yourself plenty of altitude (1,000 ft. +) so there is plenty of room to pitch down and descend toward lower terrain at a safe airspeed through any downdrafts.

48. Operations at Remote Landing Sites • Keys to Safety • Acquire Proper Training • Practice at easy sites to • gain proficiency • Fly in pairs/groups • Know the performance capabilities and limitations of your plane and yourself. • Study the weather • Have a contingency plan

50. Special considerations for backcountry airstrip operations: • Weather and surface conditions can change by the hour. • Carefully calculate takeoff/landing distance & performance data using • POH charts. Add a 50% safety margin to all published numbers. • Download passenger/cargo weight for the density altitude. Make two trips if needed. (Heavy aircraft need longer runways.) • Must be proficient in short and soft field techniques. Practice them. • If able, test the wind and inspect surface conditions first with a low pass. Then go-around and land after making a second approach. • Be prepared to camp if there’s bad weather or mechanical issues.