«Mountain Flying by K. Truemper Acknowledgment: We thank Darrel Watson very much. He reviewed a ﬁrst draft and suggested a number of improvements. ...»
Recently, sectionals have begun to provide contact frequencies for some MOAs that result in something akin to ﬂight into C space. We declare the intentions, are assigned a transponder code, and follow the instructions of the military controller. We should make sure to request permission for any deviation from the assigned altitude or course. Just telling the controller the entire planned route through the MOA at the ﬁrst contact is not good enough. Another recent development are grey-shaded Special Military Activity areas.
For transit, we must establish contact on the frequency listed on the sectional unless we desire to be mistaken for a drug runner.
2.5 Endurance The legally required minimum endurance for day VFR, which is 30 min beyond the destination airport, is not even close to suﬃcient, due to the vagaries of mountain weather and winds. A good rule is 1 hr of fuel beyond the planned ﬂight time, and 1 1/2 hrs if the route has few nearby alternate landing sites or if the weather is potentially unstable.
3.1 Turbulence It is rare that the approach to landing does not encounter some turbulence. To minimize the eﬀect, we should plan a comparatively steep descent to the destination airport.
Such an approach also provides a good overview over the terrain near the airport.
3.2. Traﬃc Pattern At uncontrolled airports in mountainous terrain, we should not expect pilots to adhere to the published traﬃc pattern. Instead, we should count on any pattern, on any entry, and even on use of runways in both directions. The key to a safe approach and landing is monitoring of the traﬃc frequency, repeated broadcast of our position, and watching, watching, watching for traﬃc. Even on the ground, we should announce all steps such as clearing the runway or taxiing across another runway, due to the topsy-turvy way runways are sometimes used.
3.3 Landing Speed When the density altitude of the airport is high, the groundspeed during landing is well above the indicated airspeed. When in that situation a gust factor is added to the indicated airspeed due to shifting winds, the groundspeed at the moment of touchdown becomes even higher. Thus, slowing the plane down after touchdown may require an extended rollout. For example, suppose the density altitude of the airport is 9,500 ft. If the landing speed is 50 kts plus a 5 kts gust factor, then, according to the formula for TAS given in the next section, the indicated airspeed IAS of 55 kts represents a true speed TAS = [1 + ((1.5)(9.5)/100)]55 = 63 (= 63 kts). Suppose we have a 10 kts headwind as we land. Then we touch down with a groundspeed of 63 - 10 = 53 kts. In contrast, a normal landing speed of 50 kts in smooth air, at sea level, and with a 10 kts headwind produces a groundspeed of 50 - 10 = 40 kts. Eﬀectively, the normal landing groundspeed of 40 kts in smooth air at sea level has become 53 kts. Since the kinetic energy of the plane increases with the square of the groundspeed, the energy that must be dissipated during the rollout by the drag of the airplane and by the brakes, is increased by 76%. Thus, the rollout is much longer than usual.
4. Two More Formulas Here are two additional simple formulas. They give reasonable estimates for the true airspeed and the course correction for crosswind. En route, we can compare the true airspeed with the groundspeed displayed by the GPS radio to get an idea how far forecast winds aloft diﬀer from actual winds. The course correction formula comes in handy during ﬂight planning.
4.1 True Airspeed Up to 15,000 ft density altitude, true airspeed is larger than indicated airspeed by approximately 1.5% for each 1,000 ft of density altitude. The formula below expresses this relationship.
TAS = [1 + (1.5D/100)]IAS where TAS = true airspeed in kts IAS = indicated airspeed in kts D = density altitude in 1,000 ft For example, if IAS = 95 (= 95 kts) and D = 10 (= 10,000 ft), then TAS = [1 + ((1.5)(10)/100)]95 = 109 (= 109 kts).
4.2 Crosswind Correction The magnetic heading is the magnetic course plus or minus the course correction for crosswind. That correction, in deg, can be estimated as follows.
CC = CW/K where CW = crosswind in kts K = factor depending on plane speed (K = 2 for 100 kts; K = 3 for 150 kts, K = 4 for 200 kts) For example, if the crosswind is CW = 10 (=10 kts) and the plane does 100 kts, then K = 2, and CC = 10/2 = 5 (= 5 deg) is the correction for the crosswind.
This is the end of the summary. I have tried to cover the most important aspects of safe summer ﬂying in mountainous terrain. But the summary is not complete: It does not tell about the excitement of an early morning takeoﬀ from a mesa into a clear sky, with mountain tops tinged red by the ﬁrst rays of the sun and with dark valleys below; does not speak of the peace and serenity of a midmorning ﬂight across a majestic mountain range topped with snow. And does not even mention the great feeling of a slow descent into an airport nestled on a picturesque mountain side, with friendly FBO folks and fellow pilots