Mountain airfield dangers - discuss

[Philbennett]

Not sure what is classed as a "mountain" globally but if we might think its terrain +2000ft AMSL the UK isn't awash with airfields at this height. What are we missing from a piloting perspective?

 

[Vance]

Not sure what is classed as a "mountain" globally but if we might think its terrain +2000ft AMSL the UK isn't awash with airfields at this height. What are we missing from a piloting perspective?

This is a very big question and the Rotary Wing Forum limits posts to a thousand words.

The best advice is to get training from a flight instructor with mountain flying experience.

The FAA has some excellent tips on mountain flying here:

https://www.faa.gov/regulations_pol...ls/aviation/media/tips_on_mountain_flying.pdf

In my opinion it is well worth reading.

The Mountain Flying Bible by Sparky Imeson is an excellent reference and available from Aircraft Spruce and Amazon.

 

[Resasi]

Mountain flying and flying in and out of airfields in the area will be subjected to the dangers of density alt, dangerous mechanical turbulence associated with updrafts, downdrafts, horizontal and vertical rotors; decreased oxygen at alt.

Many gyros have a less than stellar rate of climb making them particularly vulnerable to the various air movements around mountainous terrain. Winds funnelling through valleys can produce pronounced higher velocities due Venturi effect.

The less stable air, due all the above, can also produce sudden fogs and decreased visibility at very short notice. When doing some single seat training at N Wales airport which is right beside a cliff and the sea, on a bright sunny day, the orographic fog could suddenly start streaming over the field. I was amazed at how quickly it shut us down, then a short while later had cleared.

As you say not a great deal of very high ground here but enough in the Lake District, Pennines, Cheviots to keep one on your toes. Over in the US plenty of very high ground. Of the over 200 highest major summits of the United States, 88 are located in Colorado, 49 in Alaska, 22 in California, 14 in Wyoming, 8 in New Mexico, 5 in Utah, 4 in Nevada, 3 in Montana, 2 in Washington, 2 in Hawaiʻi, 2 in Idaho, and 1 in Arizona and we are talking ranging from 11000’ to 20,000’.

Flying in mountainous terrain is light aircraft is a whole new area that one should learn about if flying around high ground. Even airliners have been effected. A BOAC departing Tokyo flew near Mt Fuji and was ripped apart by a rotor generated by winds round the mountain
Flight 911’s filed flight plan had called for a southerly takeoff followed by a 40-degree right turn to head southwest toward Hong Kong. The commander of flight 911before takeoff, had requested and received permission from air traffic control to make a close pass just to the east of the volcano before returning to the designated airway.

Just southeast of Mt. Fuji, 911 flew into a monstrous standing rotor caused by Fuji’s “mountain wave.” The gusts exceeded design limits subjected the plane to momentary gravitational loads in excess of +7.5G, killing some of the passengers, particularly those with seat belts unfastened. A passenger's video camera, recording at the moment of upset, malfunctioned skipped two frames under the massive G-load, then briefly captured blurred images of the cabin interior before it abruptly stopped filming.

The loads ripped off the tailfin smashing it over against the left horizontal stabilizer. The stabilizer broke away, causing the plane to pitch steeply upward the sudden pitch-up over-stressing all four engine pylons to breaking point. The engines separated from the wings, followed almost instantaneously by the empennage as far forward as the rear exit doors. As the airliner began spiraling down the wings broke up. From16,000’ the shredding airliner came down streaming fuel and smoke, then baggage and passengers until smashing into the base of the Mountain.

Later that day a US Navy Skyhawk taking part in search and rescue efforts in the area flew into the same mountain wave that had brought down the 707. Despite encountering load fluctuations ranging from -4 to +9G, the pilot managed to regain control and reported what he had encountered. Japanese investigators set up a scale model of the terrain around Mount Fuji then ran wind tunnel tests to determine what kind of turbulence might have existed on the lee side of the volcano. They found strong winds blowing over the cone created an area of unstable air extending up to 12 miles in the wake of the mountain, as well as upward from the summit to an altitude of 16,000 feet with localised wind shear within the unstable area extreme enough to rip the 707 apart.

Steve Fosset was killed while mountain and the NTSB reported the probable cause was an inadvertent encounter with downdrafts above mountainous terrain that exceeded the climb capability of the Bellanca Super Decathlon he was flying. Downdrafts, high-density altitude and mountainous terrain all contributing factors.

I’ve also seen mountain wave cloud formations extending back miles from both the Rockies and the Andes.

 

[anthom]

Spot on Leigh.
We routinely operated from mountainous helipads up to 19,000 ft MSL in the HimalayasL The only aircraft that we could do so in then (I'm talking 30 years ago) were the Lamas and MI-17s. The picture below was taken at a helipad at 14,700 ft. Mostly used the valley winds to plan and execute our approaches. Sometimes, (as the picture depicts), we would turn and land in a cul de sac, with no overshoot possible.. We operated on very slim power reserve margins. I've lost many of my friends who were not fortunate enough.

Power is king!

 

[dinoa]

Distorted horizontal reference when flying below the ridge line of surrounding terrain.

Flying close to terrain against fall line that is rising. Similar to flying into a box canyon in a fixed wing. While the gyro can complete a u turn in a short radius it doesn’t have the ability to convert speed to height like a fixed wing. The perception of rising terrain may not be obvious.

 

[Resasi]

The perception of rising terrain may not be obvious.

Can be very insidious. My first venture into the local training area around Rissington in a Bensen had me puzzled. I was around 2,000’ and could not understand why with no throttle change I seemed to be losing then gaining speed at what I thought was constant alt. It took me a while to realise I was inadvertently contour flying with its associated climbs and descents.

 

[WaspAir]

There's plenty of energy, but not plenty of air density or oxygen, in the high altitude environment.

My suggested recipe for preparation is to seek out a glider CFI who has done some serious wave flying. He/she can help you to imagine ("see") what the flow may be doing and plan accordingly. It's pretty routine for gliders to get up truly high in the mountains, and with no engine at all, you need to understand what's going on. Last time I checked, the Colorado state record for glider altitude was above 44,000 feet. Sustained climb rates of over 2,000 fpm for 800 pounds of aircraft with zero horsepower are routine in standing waves, with nearby downdrafts to match. Rotor turbulence once caused one of our tow planes to come back with more dihedral in one wing than the other.

(By the way, the current world glider altitude record, set in the Andes in the pressurized Perlan 2 glider, is about 76,000 feet, up in U-2 / SR-71 territory. You need to respect Mother Nature when she decides to create conditions like that.)

 

[loftus]

Can be very insidious. My first venture into the local training area around Rissington in a Bensen had me puzzled. I was around 2,000’ and could not understand why with no throttle change I seemed to be losing then gaining speed at what I thought was constant alt. It took me a while to realise I was inadvertently contour flying with its associated climbs and descents.

I've noticed this effect even flying from flat terrain into moderately hilly and rising terrain, as when I flew from Florida to Georgia.

 

[Tyger]

From Tips on Mountain Flying:
"At sea level, the standard temperature is 59 degrees Fahrenheit [15ºC]; however, at 10,000 feet MSL, the standard temperature is only 23 degrees [-5ºC].
This means that at Leadville, Colorado (elevation 9,927 feet) when the temperature is only 24 degrees, the density altitude is already above the field elevation."

 

[dinoa]

The slope of terrain is very difficult to judge at height. A rule of thumb is that slope appears to be about half of what it really is. This is important when choosing a place to land.

 

[Tyger]

It's also worth mentioning that, for those not acclimatized, a relatively short spell around 10,000 ft can make many people feel pretty lousy, even though that's below the required-oxygen altitudes.

https://www.faa.gov/pilots/safety/pilotsafetybrochures/media/hypoxia.pdf

 

[WaspAir]

It's also worth mentioning that, for those not acclimatized, a relatively short spell above 10,000 ft can make many people feel pretty lousy, even though that's well below the required-oxygen altitudes.

Before you feel lousy, you may have impaired skills and judgment. Hypoxia can produce euphoria and degradation of your faculties long before unpleasant effects are noticed (headaches being a common one). It's a bit like alcohol in that your judgment about the quality of your own judgments is one of the first things to go.

A sea-level dwelling smoker can be hypoxic on the ground and have really poor night vision where I live and fly.

 

[WaspAir]

P.S. VFR night flight in mountainous areas can be a pretty dumb thing to try.

 

[Tyger]

Before you feel lousy, you may have impaired skills and judgment. Hypoxia can produce euphoria and degradation of your faculties long before unpleasant effects are noticed (headaches being a common one). It's a bit like alcohol in that your judgment about the quality of your own judgments is one of the first things to go.

A sea-level dwelling smoker can be hypoxic on the ground and have really poor night vision where I live and fly.

Yes, it affects everyone a bit differently.
A few years ago I flew commercial from NYC (sea level), met a friend in Phoenix (1000 ft), then drove to Taos, NM, spending two nights at 7000 ft before hitting the ski slopes. Base lodge at Taos Ski Valley is 9300 ft. He was sick as a dog within an hour, whilst I felt fine (if a bit winded at times).

 

[Vance]

It's also worth mentioning that, for those not acclimatized, a relatively short spell around 10,000 ft can make many people feel pretty lousy, even though that's below the required-oxygen altitudes.

https://www.faa.gov/pilots/safety/pilotsafetybrochures/media/hypoxia.pdf

After flying for two hours at 9,000 feet density altitude I found I could not remember the name of the airport for my radio calls. I had a Garmin 696 that had the information. I don't smoke; I do live at sea level and have had a traumatic brain injury. I am old and not in very good shape. It was time for a rest.
Now if I am going to fly at night or over 8,000 feet density altitude I use oxygen.

 

[anthom]

If one wants to venture into the challenging realm of mountain flying, there is no better way to do so than fly with someone that has done it before. Flying in the mountains can be accomplished if one truly understands the limits of man and machine. We used to go from our base at 250 ft MSL to helipads at 10,000 plus in a matter of 45 minutes. We used supplemental oxygen to avoid hypoxia.

As far as gyroplanes are concerned, I'm not sure if they can handle the severe turbulence and downdrafts with unpowered rotors. Personally, I do not see the need to venture into the mountains in gyroplanes unless weather conditions are pristine. If I do, I'd do so with a machine that has plenty of reserve of power. We had SOPs to cross mountain ridges at 45 degrees so as to be able to turn back in case the crossing was unsuccessful. Flying without an exit plan or the ability to turn around is IMHO like playing Russian Roulette.

Low clouds and poor visibility are common, lack of a proper horizon can be detrimental without proper instrumentation. At the very least, an AH is a must. I remember one memorable flight when I had to do a vertical climb through zero visibility through 4000 plus feet to get out of a self-inflicted trap. One of the stupidest mistakes during my flying career.

Mountain flying with proper training, preparation and equipment can be a fantastic experience.

 

[Resasi]

Low clouds and poor visibility are common, lack of a proper horizon can be detrimental without proper instrumentation. At the very least, an AH is a must.

Part of my military flight training was limited panel. We had to blank out our six pack one by one.

With only needle ball and airspeed, one got the ‘leans’ within a fairly short time. This varied with the individual, and could be left or right, ie a tendency for the individual to begin a turn in order to try and stay level.

It was somatogravic* illusion that resulted in a turn either left or right, that rapidly steepened until control was lost...generally within 45 seconds to a minute. Pretty sobering stuff.

*Somatogravic illusion is the tendency – in the absence of visual references – to incorrectly perceive acceleration as an increase in pitch attitude, a perception that can lead pilots instinctively to make nose-down inputs even if the aircraft is flying level.

 

[Tyger]

Somatogravic?
Sounds a bit like the recent infamous Calabasas crash...

 

[DavePA11]

I'm getting use to higher elevation now after moving to home at 8,000' in Colorado. Base airport is down on the plains at 5,000'.

 

[Tyger]

How would you feel about flying a gyro again out there, Dave?