2
$\begingroup$

When flying under visual flight rules (VFR), pilots have to be able to see far enough away to be able to avoid running into other aircraft or the ground. Therefore, VFR flight requires good visibility with a high (or no) cloud ceiling; this is known as visual meteorological conditions (VMC). It also requires that pilots avoid clouds like the plague, since clouds (on Earth, at least) tend to be on the opaque side, and a cloud that you can't see through could potentially be hiding something that it would be very bad to run into (such as someone else's aircraft).

Avoiding clouds is easy enough during the daytime, if the weather is good (the big white things tend to be fairly visible as long as you aren't actually inside one), but, in many countries (including such biggies as the US, France, and Australia), VFR flight is also permitted at night. As clouds are not usually polite enough to illuminate themselves for the benefit of nearby pilots, they tend to blend in rather well with the dark sky (except sometimes when bright moonlight is present), the only hint of their presence being that they occlude background stars (which provides absolutely no information about whether those stars are being hidden by a small cloud close by, or by a big cloud further away, and depends on the stars being easily visible to begin with [which is not always the case, even at night]).

So how do pilots avoid clouds when flying VFR at night?

$\endgroup$
  • 1
    $\begingroup$ Moonlight is more common, and more useful for seeing clouds, than you might think. Other than that, you use eyes, weather forecasts, and common sense to avoid flying when there might be clouds you can't see. $\endgroup$ – jamesqf Jan 24 at 0:29
  • $\begingroup$ Clouds have a nasty habit of popping up from place to place even in good weather - no amount of weather-forecast watching can assure the absence of clouds. And, while moonlight might well be common, the lack of moonlight is also common - what if it's the new moon or a thin crescent, or the moon is obscured by a high-altitude cloud ceiling, or the moon hasn't risen yet / has already set for the night? $\endgroup$ – Sean Jan 24 at 0:33
  • 1
    $\begingroup$ Depends on where you do your flying. In most of the western US (where I've done the great majority of my flying), clouds are fairly predictable - e.g. if there are clouds on a summer night, they are going to be cu-nimbs full of lightning. Then, as with those other situations, you stay on the ground :-) $\endgroup$ – jamesqf Jan 24 at 5:44
3
$\begingroup$

I will caveat my answer by saying that most of my night flying has been under IFR, but because of that I have lots of experience going in and out of clouds at night.

It starts with a good weather brief, and don’t forget to ask for PIREPS that might cover areas further away from the field. True enough the bases can be ragged, and little puffies can lurk in unexpected places, but if you know where the layers are called you are well on your way to avoiding being at the same altitude.

To add to one of the comments, moonlight is helpful, but so is ground lighting. At night distant clouds can be difficult to see, but you can use ground lighting to gauge where the coverage is. For example, if your eyes can trace a lighted road off in the distance, but at approximately 20 degrees below the horizon the car lights become blurry, then disappear, it is probably because of a cloud between you! Angle away, or descend below the deck until the horizontal visibility range increases.

If you start skimming clouds you will know it immediately because your anti-collision light will blossom and reflect red all over the inside of the cockpit. If you still have ground lights in sight and you know the clouds are stratified, I would start a gentle descent. If there are a lot of vertical buildups and you pop into one and lose sight of the ground, make a level 180 and get out of there. Most non-instrument rated pilots are taught to deal with inadvertent IMC in this way.

As I mentioned in my answer to your other question, make sound risk decisions. If you are uncomfortable with the weather conditions or your ability to remain clear of clouds, then choose to not fly VFR at night. But once you get a few night flights under your belt I think you will find that they can be very enjoyable when conditions are good. It opens up a whole new perspective on things!

|improve this answer|||||
$\endgroup$
2
$\begingroup$

One thing you can do to minimize the risk of cloud encounters at night, besides the obvious one of staying below reported or forecast cloud layer altitudes, is to maintain a positive dew point spread in the air mass you are flying in, to the extent you can, since cloud usually won't form until the spread becomes zero.

So if the dew point is 8C and it's 20C on the surface, a 12 degree spread, I would avoid climbing any higher than an altitude that gives a 2 deg C spread, about 5000 ft AGL, which should give a 1000 ft margin below any cloud that may form. Of course, if you end up flying into more humid air with a higher dew point, you're back to square one, so you need to take into account factors like potential changes in humidity (flying from over dry land to over a large lake for example).

Beyond that, it's a case of being good at making 180 degree turns in IMC when the ground disappears. In night VFR, if you encounter a cloud the priority is to return to the clear air you were in just before, so you simply make a level 180 degree turn on the gauges and wait to break out, then descend (you want to avoid climbing/descending turns in IMC when you only have a couple hours of time under the hood).

|improve this answer|||||
$\endgroup$
2
$\begingroup$

Starlight, moonlight and light pollution from the ground are often adequate to see where the clouds are almost as well as you can during the day. But not always - if there's a high overcast to block the stars and a new moon and you're out in the back country or over the ocean, it might as well be IMC. Pilots have to use their judgement and not fly VFR at night even in VMC if conditions are such that they can't be reasonably assured of maintaining VMC.

|improve this answer|||||
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.