Lesson

WeatherXplore Low Ceiling / Mountain Obscuration

Low Ceiling / Mountain Obscuration

Let’s put this in simple terms:

  • Low ceilings are a problem for all pilots.  VFR pilots are tempted to fly lower to terrain, or possibly closer to the clouds than they should.  Deteriorating ceilings and visibility can easily lead to spatial disorientation and a loss of control of the aircraft.  Instrument rated pilots are left with less time to see and avoid terrain as they exit the clouds.  The bottom line; low ceilings are bad for everyone.
  • Low ceilings in mountainous areas often leads to “mountain obscuration” (you can’t see the mountains that are totally or partially obscured by clouds.  Clouds are soft, mountains are not, thus the problem if we are flying through a cloud that is hiding a mountain and accidentally find the mountain.

In more scientific terms:

  • Low ceilings are often caused by stratus clouds
  • Stratus clouds and fog are very similar, and for our purposes, we can say fog is just stratus clouds at ground level.
  • One of the most hazardous conditions rather than just a “low ceiling” (say a 500′ overcast ceiling) is a case when the vertical visibility is reduced (i.e. VV500 is worse than OVC005 since the former implies a ceiling of 500′ but also implies reduced slant range visibility all the way to the ground as shown in AC 00-06B Figure 16-6).

The Scenario

You depart VFR with clouds 1,900′ scattered for a short 35nm to a nearby airport to get fuel.  As you continue there you notice the ceiling becoming more solid and the clouds seeming to get lower, along with reduced in-flight visibility.  You would normally turn around, but the airport is only 4nm away at this point and you didn’t really have much fuel when you took off (so turning around isn’t a great option, although it would be the right thing to do) and you have even less fuel onboard now 20 minutes into your flight.  The forecast was calling for 10sm visibility at your destination airport despite it looking terrible up ahead, so you think “hey, I should see clear air and better visibility any minute now.”  As you continue over the next mile you cannot see much terrain in front of the nose of the aircraft and you are starting to lose ground contact.  You begin looking at the ground straight down below you more than over the nose and at your instruments.  You try to keep the wings level and find the airport by looking straight down for it below you.  You notice the engine RPM seem to increase and the wind noise is also slightly louder.  You do not feel like you are turning and when you look back at your instruments you see increasing airspeed, decreasing altitude, and the attitude indicator is tilted, yet you feel like you should be straight and level.

This exact scenario (and similar scenarios of low ceilings and visibility) have claimed the lives of thousands throughout the history of aviation.  There’s only one way out of this scenario.  It is flight by reference to instruments to recover from an unusual attitude and turn the aircraft back towards better weather.  The best solution to this problem is to avoid a situation like this in the first place.  If it looks bad up ahead, it is.  No need for you to “go take a look”.  Turn back early, as soon as you’re thinking turning back might be an option, that is the time to do it.  Work with your instructor to help you recognize what situations and forecasts may lead you into a situation such as this.  Fly with a wide safety margin over the legal VFR minimums to help avoid becoming a statistic.