You have planned a cross-country flight on a warm spring morning. Your course includes a mountain pass, which is at 11,500 feet MSL. The service ceiling of your airplane is 14,000 feet MSL. After checking the local weather report, you are able to calculate the density altitude of the mountain pass as 14,800 feet MSL. Which of the following is the correct action to take?单项选择题
A
Continue as planned because mountain thermals will assist your climb.
B
Replan your journey to avoid the mountain pass.
C
Continue as planned since density altitude is only a factor for takeoff.

Question

You have planned a cross-country flight on a warm spring morning. Your course includes a mountain pass, which is at 11,500 feet MSL. The service ceiling of your airplane is 14,000 feet MSL. After checking the local weather report, you are able to calculate the density altitude of the mountain pass as 14,800 feet MSL. Which of the following is the correct action to take?单项选择题

A

Continue as planned because mountain thermals will assist your climb.

B

Replan your journey to avoid the mountain pass.

C

Continue as planned since density altitude is only a factor for takeoff.

BlackTom AI · Accepted Answer

Rephrasing the scenario helps frame the decision: you’re flying through a mountain pass at 11,500 ft MSL, with a density altitude calculated at 14,800 ft MSL, and your airplane’s service ceiling is 14,000 ft MSL. This means the air is effectively thinner than the aircraft is certified to operate safely at, which degrades climb performance and raises the risk of not clearing obstacles in the pass.
Option A: Continue as planned because mountain thermals will assist your climb. This is not a reliable or safe assumption. While thermals can provide lift in certain conditions, they are unpredictable and insufficient to overcome a density-altitude situation where required climb performance is compromised. Relying on thermals here could lead to an insufficient climb rate and entering the terrain, especially in a high pass with limited margin.
Option B: Replan your journey to avoid the mountain pass. This option directly addresses the heightened density-altitude challenge. With a density altitude of 14,800 ft and a service ceiling of 14,000 ft, the aircraft may not be able to achieve the required obstacle clearance in the pass, so rerouting to lower terrain or an alternative route enhances safety and reduces the risk of an overrun or an inability to climb.
Option C: Continue as planned since density altitude is only a factor for takeoff. This is a misconception. Density altitude affects all phases of flight, including en route and in-passing climbs, due to reduced engine power (in carbureted or certain engines), reduced prop efficiency, and poorer aerodynamics. It is not limited to takeoff scenarios.
In summary, recognizing that high density altitude reduces climb performance and increases the likelihood of not clearing terrain in a mountain pass supports choosing a safer routing, i.e., avoiding the pass rather than pressing on with the original plan.

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