|Those of us fortunate enough to live and fly in the Southwest know what it has to offer: beautiful skies, landscape and weather. We fly over mountains cut by streams with ribbons of green. The streams sometimes flow to green valleysbeyond which may be the open desert.
We see it all by air, and it never grows old; It just grows on you. The sheer vastness inspires awe in even the most jaded pilots. Viewed from the cockpit, it seems you could fly forever without reaching its end.
By flying in the Southwest, one can come face to face with mountain peaks and pull distant mesas impossibly close. To be unfettered from earth in an aircraft is a wonder. To be unfettered over the great Southwest is a step beyond.
But for the aviator who lives and flies here, enjoying the skies of the Southwest does not come without a cost. Aviators must invest the time to gain aeronautical knowledge about the possible dangers of the land where a few buffalo are again roaming and the deer and the antelope still play.
Those who fly these skies must be familiar with density altitude and how it affects our silver birds of flight. A takeoff can land you in a world of hurt.
Simply defined, density altitude is pressure altitude corrected for nonstandard temperature. Pilots often confuse pressure altitude with barometric pressure or field elevation. Pressure altitude can always be obtained by turning your altimeter window to 29.92 and reading the altitude.
High density altitude is so insidious. You can't see it, but it is there. If you ignore it, you may meet it three-fourths of the way down the runway, bringing the sinking feeling that you won't make it over the trees. It's no pun to say that it is not an uplifting experience.
The wings, elevators, rudder and propeller are all airfoils responding to air flow. They lift, guide and power an aircraft. When the density altitude is high, the performance of airfoils is degraded, giving less lift and thrust. Engine power is reduced due to less dense air. Low air pressure in the cylinders requires less fuel to give the ideal mixture, but less fuel and air means less power.
Maximum aircraft performance is at sea level on a standard day. Turbocharged engines provide sea level thrust to their critical altitude, but the airfoils on a turbocharged aircraft suffer from density altitude just like those on the normally aspirated aircraft. A standard day at sea level is 15 degrees centigrade (59 degrees Fahrenheit) and an atmospheric pressure of 29.92. Since temperature decreases at a standard lapse rate of 2 degrees centigrade (3.5 degrees Fahrenheit) per thousand feet, a runway at 5,000 feet has a standard temperature of 41 degrees Fahrenheit. Does that sound like a winter day? Yes. All the rest are higher density altitude days.
High density altitude requires more runway for take off, landing and climbs. It also makes for lower service ceilings. This can all spell trouble when mixed with mountains.
At an airport with an elevation of 5,000 feet and a temperature of 100ûF, the aircraft performs as it would at 9,000 feet on a standard day. If the service ceiling is 15,000 feet you may max out at 11,000 feet on a hot day with full weight.
One summer day, I departed from Las Cruces, NM in a C-182 with four on board. We were under gross weight, and Runway 30 was plenty long for the take off. But after 70 miles, we had only climbed 1,000 feet. That would make for a pretty big traffic pattern.
A friend of mine in East Africa took off from a grass airstrip in a C-206 with five aboard. The strip was at over 7,000 feet elevation on a hot day near the Serengeti Plain. He fell victim to density altitude trying to avoid a ridge off the departure end of the runway and left me with the unpleasant responsibility of flying his remains part of the way back to the US. Respect density altitude. Lighten your load by carrying less fuel and baggage or fewer people. Plan your departure early in the morning when it's cooler. In your preflight preparations, check the performance tables in the aircraft POX for take off distances at high temperature. Don't just push the throttle forward and hope you will make it safely into the air. Wishful thinking never helped anyone, least of all an aviator.
Due to the combination of open and mountainous terrain, another prominent presence in the Southwest is the strong, gusty, variable winds. This also includes the "dust devil," a swirling upward rising parcel of air. I encountered one on short final with a student, and it was a wild ride for a few seconds. I took the controls andwith full power in the go around modewas able to fly out of it.
Strong winds creating mechanical turbulence from trees, ridges and buildings can be treacherous. An aircraft about to touch down can be lifted 25 feet into the air with decaying airspeed. The only remedy is instant power and a go around.
It is best if you choose not to tangle with strong, gusty winds. Carry a crosswind component chart with you and know if you and your aircraft can stand the test. The crosswind component can be estimated by the following rule of thumb: If the wind is up to 30 degrees off the runway heading, one-third of the wind speed is the crosswind component. From 30 degrees to 60 degrees it is two-thirds the wind speed and 60 degrees to 90 degrees consider it the full wind speed.
The vast Southwest can be a harsh environment in the summer or winter, should a forced landing be necessary. The wise pilot carries survival gear for the season in which the flight is made. After an off-airport landing in winter, survival may not be possible without warm clothing. The same is true of the hot summer without a sufficient water supply. The survival kit should includeamong other thingsmedical supplies, a signaling mirror, waterproof matches, flares, and space blanket. In this region, the temperature can be thirty to forty degrees colder at night than during the day.
Before a flight, give thought to how you would survive if the great Southwest gobbled you up. I vividly remember flying in 1992 over the southwest corner of New Mexico in a C-206. Suddenly, the oil pressure went to zero and a rod went through the crank case. I managed to land on a dirt road with no damage to the aircraft. The temperature was near 100 degrees, and I was thankful for the water on board while I waited for assistance.
Mountain flying is another serious consideration in Southwest Aviation. However, the scope of that subject is so large that I may dedicate an entire future article to it.
The great Southwest is beautiful and challenging. The beauty we have always, but our proficiency and knowledge to meet those challenges can fade and must be constantly exercised and renewed.
Cordell Akin is a CFII, MEl with a total of 10,000 hours and 3,000 hours as a flight instructor. He spent 15 years in East Africa flying a C-185 and a P-210. He is the owner of Akin Air at Coronado Airport in Albuquerque.