Mountain Flight
ASSUMPTIONS FOR A MOUNTAIN FLIGHT
These are the assumptions on which this document is based:
- The flight will be flown that meets the minimum weather criteria, described herein.
- The flight will be flown in daylight.
- The flight will be flown using Visual Flight Rules (VFR).
- The aircraft to be used will have sufficient performance for the mountain flight.
- The flight will be made without use of supplemental oxygen.
- Navigation will, primarily, involve pilotage.
FOUR MAJOR PARTS OF A MOUNTAIN FLIGHT
The mountain checkout is divided into four major parts.
- Ground training session. Determine if the current and forecast weather situation for the route to be flown is satisfactory for a safe, comfortable mountain flight, based on the criteria described in this document; and ensure that sufficient daylight will be present for the duration of the flight. Discuss factors that may affect the flight including winds, weather, terrain, FARs, navigation, nightfall, aircraft performance, venturi effect, hypoxia, box canyons, rising terrain, downdrafts, updrafts, escape plans, human factors, ridge lift, "get-home-itis," etc.
- Plan the flight and file a flight plan.
- Preflight the aircraft, check the weight and balance, inform the passengers.
- Fly the planned route, notifying Flight Service of any deviations in the proposed route, times, or altitudes. Always have an escape route.
WEATHER CHECK
Cloud Bases
Although a check of the current and forecast weather needs to be done for any flight, mountain flight weather is more critical. Cloud bases must be high enough along the route to provide sufficient room to cross passes and fly the route.
The altitude for crossing a pass should be sufficient for the conditions, and this usually means the aircraft should be 500 to 1,000 feet above the point where the crossing is flown. The higher the headwinds, the higher the necessary altitude should be in case downdrafts are encountered during the crossing.
Wind Direction
The direction of the wind is critical in the mountains because it follows the surface. If the ground rises, the wind flows upward. If the ground slopes away from the wind direction, the wind flows downward. This action can be compared to the way water in a stream flows over rocks. When wind flows over smooth hills and mountains, it tends to flow smoothly. When it flows over a cliff, it tends to tumble over the edge in a turbulent manner.
Wind Speed
The effect of wind speed is important. As a rule of thumb, a normally aspirated, single-engine aircraft should not fly in mountain when the wind speed exceeds 30 knots. The actual "no-go" wind speed limit that a pilot chooses depends on many factors including the type of aircraft flown, the type of terrain, the shape of the valleys and passes to be flown, the elevations to be crossed, etc.
Venturi effect
The venturi effect causes air to increase its speed when passing through a narrow opening, slot, or pass. For example, if the wind speed over level ground is 20kts, when that wind passes through a pass, its speed will increase. An aircraft flying into the wind when crossing a narrow pass will probably experience higher headwinds than it would over open country. Since high winds usually result in downdrafts on the leeward side of a pass, the dangers are that the ground speed is reduced by the
faster moving wind, and severe downdrafts are often present.
Evidence of High Winds
Evidence of high winds in the mountains can sometimes be seen when there is sufficient humidity in the air to allow clouds to form. Cap clouds form when air is swiftly thrust over the top of a peak. Standing lenticular clouds (lens-shaped clouds that stay in the same location in the sky) are the result of a ripple effect of the wind passing over peaks. The air on the upwind side of standing lenticular clouds is rising and on the downwind side, it is descending. Fractured and torn-looking
clouds may indicate turbulent winds.
Daylight
The flight must be completed in daylight. For higher-flying aircraft that cross the mountainous areas, this is not as critical an issue. However, for our purposes, any flight in the mountains must be done in daylight because the peaks and passes are not lighted, some navigation aids may not available due to high terrain, communication with Air Traffic Control (ATC) facilities may be limited or non-existent due to terrain, and terrain visibility may not be possible in darkness. Night
vision is reduced at night at high altitudes where supplemental oxygen is unavailable or not utilized. There have been many mountain accidents caused by aircraft flying in mountainous areas at night. If a pilot is caught in the mountains near the end of the day, the best action is to find a place to land while there is still sufficient light, and wait until the next suitable day to fly.
FARs
Several Federal Aviation Regulations (FARs) are in effect in mountain areas.
A plane can fly above 14,000 for only one-half hour unless the pilot uses supplemental oxygen and it is available to the passengers. Above 15,000 feet, supplemental oxygen must be used by all occupants of the aircraft. FARs restrict flight over some national parks and wildlife areas.
Climbing to a Pass
Climbing up to cross a pass is a critical phase of the flight. If the turbulence is makes the flight uncomfortable, the pilot should return to base. If the plane cannot climb high enough to get over the pass safely, the crossing should be canceled. Climbing toward a pass should be done at a maximum aircraft performance setting to achieve the best rate of climb. As the altitude increases, the best rate of climb will decrease until it is near the stall speed. At this point, the aircraft is
near its ceiling. This maximum altitude will probably be lower than that shown in the pilot's operating handbook because of engine wear, etc.
Using Ridge Lift
An aircraft can improve the climb by flying on the windward side of hills and mountains. If the route to a pass has a hill or ridge that is perpendicular to the wind or nearly perpendicular, the pilot can maneuver the plane to fly along the face of the hill or ridge so that it can take advantage of the rising air. When the rising currents die out, as indicated on the vertical speed indicator, the pilot can make a careful turn in the direction away from the hill or ridge and reposition the
aircraft to catch the updraft. This can be done by flying in the opposite direction or by flying a large circle to catch the updraft where it was first encountered.
Crossing a Pass
Crossing a pass is a critical part of a mountain flight. As the plane approaches the pass, the pilot should have an escape route planned in case it becomes impossible to get across. Sufficient altitude must be achieved prior to nearing the crossing point. If there is any doubt that the crossing may not be safe, it is best to abort the attempt and return to base. For example, severe turbulence can cause loss of control, downdrafts can eliminate a safe crossing altitude, and poor weather on the other side of the pass can cause the attempt to be aborted. A pass can be crossed at a 45 degree angle to provide a shorter turn to the escape route in case a downdraft is encountered.
Identifying a Safe Altitude to Cross a Pass
A safe altitude to cross a pass varies, depending on the aircraft’s performance, the winds, the pilot's hypoxia symptoms, etc. One visual cue is the sight of ground beyond the pass that appears to rise as the aircraft nears the crossing point. If the ground behind the pass appears to descend or become less visible, the aircraft is descending and a safe crossing may not be possible. If the ground continues to rise beyond the pass, so that more of it can be seen, the aircraft may be climbing to a safe crossing altitude. Also, the pilot needs to be able to estimate the plane’s elevation above the pass and any peaks in the area of crossing. It may help to tip the wings to look beneath the plane to ensure that sufficient altitude is present. A plan of escape is needed in case the crossing cannot be made safely. Experience flying with a mountain pilot can be a great way to learn how to know when a safe crossing is possible.
Pilot's Mindset
A pilot must expect that a crossing may not be possible and should advise any passengers of this possibility so that they will not be alarmed if the crossing is aborted and the pilot has to return to base. A pilot should be ready to execute a turn away from the pass if there is any possibility that the crossing cannot be made safely. The pilot must have an escape plan and be ready to execute it at any moment.
Downdrafts
A pilot can experience downdrafts anywhere in a mountainous area. They are usually prevalent when the winds are from the opposite side of a pass, hill, or ridge. The pilot must recognize downdrafts by constantly checking the vertical speed indicator. When a severe downdraft occurs, the pilot must get away from it quickly by executing an escape plan.
Updrafts
Severe updrafts can be experienced, especially on the leeward side a pass. For example, if a pilot has crossed a pass from the windward side, as the plane continues beyond the summit of the pass, a mountain wave updraft may be encountered that draws the plane upward in excess of 2,000 feet per minute. Although this may not cause an immediate danger if the air is smooth, the pilot must immediately correct this situation because the plane can be drawn up into Class A airspace without clearance, the pilot and passengers may experience sever symptoms of hypoxia, and the aircraft can enter the flight path of another aircraft. There are several possible escape methods, but one that may be the safest is to slow the plane to the flap operating range, lower the flaps, and point the nose down to descend. A slip can also be used if the pilot feels proficient to execute that maneuver. The pilot must be aware that a downdraft may be encountered and be ready to raise the flaps if they are down, and to begin a maximum performance climb.
Escape Plan
An escape plan should be in the pilot's mind at all times during mountain flight. It is critical during the attempt to cross a pass. The escape plan usually involves a turn toward lower terrain and either circling to gain sufficient altitude to try crossing again, or a return to base. A pilot should never enter a “trap” where a turn toward lower elevation terrain is not possible. In this regard, a pilot needs to know how much room the aircraft requires to make a turn, and how much altitude might be lost in such a turn when the plane is already flying level at maximum performance. A turn requires additional lift to maintain altitude, and if extra lift is not available, the plane will descend. Escape Route. If the plane encounters a severe downdraft, the pilot must have an escape planned. He can turn right or left toward lower ground to exit the area of the downdraft. This applies to many situations including ground or trees that appear to be rising toward the aircraft even though the plane is in maximum climb configuration, the onset of darkness, worsening weather, flying up a canyon whose walls are beginning to narrow, etc. When an unsafe situation presents itself, the pilot should get away from the situation and know where to go to get into a safe area.
Mountain Navigation
In mountainous areas, pilotage is the preferred method of navigation because the terrain can block or distort ground-based navigation systems. GPS can be used to navigate, but a constant visual reference to the peaks and high terrain is imperative.
Hypoxia
Hypoxia is the condition experienced when insufficient oxygen is supplied to the brain. This is caused by a lack of oxygen in the environment or the inability of the cardiovascular system to provide the necessary supply, for example, when carbon monoxide is breathed. At high altitudes, the air becomes thinner, and the partial pressure of oxygen is reduced to the extent that the supply to the brain is reduced. The effect of hypoxia varies between individuals. Those who live at higher altitudes may experience less effect of hypoxia. Smokers, persons with smaller lung capacities, and persons with health problems may experience it hypoxia at lower altitudes.
Identifying Hypoxia
It is important for each individual to know the symptoms that he or she feels at the onset of hypoxia. These symptoms are the warning signs of the beginning of reduced mental acuity. There are many possible symptoms including dull headache, giddiness, tingling extremities, flushed face, etc. Whatever initial symptom is experienced, each person should remember it and take appropriate action when it occurs by going to a lower altitude or taking supplemental oxygen. Although it is possible to continue a flight when experiencing symptoms of hypoxia, the pilot should be very careful because hypoxia can cause loss of consciousness.
Box Canyons and Rising Terrain
Box canyons can take many forms. In some cases they may not be canyons at all, but are two ridges on either side of the plane that rise and close together so that the pilot is unable to execute a 180 degree turn to exit the area. The pilot may not notice that the terrain is slowly rising, faster than the plane can climb. A pilot must always be aware of the terrain around the plane and ensure that the plane does not get trapped in an area where a 180 degree turn is not possible. A plan of escape is always necessary. It is easy to forget to keep tabs on the surrounding area.
"Get-home-itis"
This is the dangerous condition of feeling the need to continue the flight in unsafe conditions. The unsafe conditions can be anything that threatens the safety of the flight. At the beginning of a flight, the pilot must know that the flight might have to be terminated and that the plane will have to return to the takeoff point or to another suitable landing place. The pilot must let the passengers know this so that they will understand the pilot's decision. The pilot must always be in
command and not yield to passenger's wishes if a safe flight cannot be assured.
PLAN THE FLIGHT
Flight planning in the mountains must take into account aircraft performance, the winds, the weather, the amount of daylight needed for the flight, the location of communication facilities such as remote communications through VOR stations, and what to do if a problem occurs. All airports along the route
should be noted so that they can be quickly found if the flight needs to be terminated early. The aircraft altitude should be predicted along the flight path so that if the plane is not climbing sufficiently, the pilot can circle to gain sufficient altitude or turn back toward lower ground and terminate the flight.
File a Flight Plan
A flight plan must be filed so that if an accident occurs, the search can begin as soon as possible. In mountains, nights are usually cool, and it is possible to get hypothermia, even in the warmest months of the year. If hypothermia is not treated in a reasonable amount of time, it can cause loss of consciousness and, ultimately, death. Injuries are not uncommon in an off-field landing, and they can cause death if a search is not begun soon enough.
Emergency Equipment
The pilot should consider carrying emergency supplies and equipment on a mountain flight. There are many sources of lists of equipment that can be carried. Perhaps the most important are water and warm clothing. The details of mountain survival is a course by itself, and is not discussed here.
PREPARE THE AIRCRAFT
Preflight the aircraft and ensure that sufficient fuel is on board. Check the weight and balance to make sure that the aircraft performance at the weight to be flown will be sufficient for the flight.
It is important to inform the passengers that the flight might not be completed if conditions are not acceptable for a safe trip. Also, let them know what to expect in the way of maneuvering through the mountains, circling to gain altitude, turbulence, hypoxia, etc. The passengers should understand that the pilot is in command at all times and that his or her decisions are final.
FLY THE PLANNED ROUTE
Notify Flight Service of any deviations in the proposed route, times, or altitudes. And remember to always have an escape route and a backup plan if the flight needs to be altered. Remember that a lot of aircraft have been lost in the mountains, and that you won't add yours to the list.