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Is there any correlation between night or day flight time and rate of accidents?

To me it seems that there should not be a difference. If an airplane needs to execute an emergency landing, it has to do it at an airport which is illuminated at night.

However, what if the pilot needs some ground visuals to navigate, for example, because the instrument are not working similar to the Air France Flight 447.

Edit

I only mean commercial airline flights done by planes such as airbus a320/321/330 or Boeing 737-800.

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    $\begingroup$ AF447 occurred in IMC. Probably would have happened in the daytime too $\endgroup$ – TomMcW Jun 14 '16 at 23:10
  • $\begingroup$ Been doing a layman's research on air India flight 855 that crashed near Bombay (Mumbai now) in new year 1978. It went down into the Arabian sea just 3 Km away after take off. The night factor (about 8.45 pm) may have contributed to the cause inconclusively pointed at pilot disorientation /instrument failure. They didn't know they were banking more and more to the left, the report says. (not the exact words). It was a Boeing 747 (not sure) bom - dubai. $\endgroup$ – Jay B Jan 17 '18 at 9:11
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First, I should reiterate that commercial flights at any time of day are extremely safe. Saying flights at night are more dangerous is like saying going to buy groceries at night is more dangerous. It may be true, but it shouldn't be something a traveler worries about.

It seems from the available data that accidents are at least more dangerous at night, even though I can't tell if accidents are more likely. Certain kinds of accidents, like weather-related accidents or disorientation, are also more common at night than during the day.

A great source for this is an incident database that you can download from the NTSB database of aviation incidents (there's a link on the page for downloadable datasets). Opening the downloadable dataset in Access lets you find statistics for whatever criteria you want. I filtered for records with aircraft operating commercially (not general aviation or commuter) with light conditions (like day vs. night) available.

In this dataset, 1562 incidents occurred during daylight, dawn, or dusk, and 635 occurred at night, or about 29% of all incidents (Incidents include procedural violations and near-misses as well as accidents that cause damage or injury). To figure out how likely an accident is at night versus the day, we would need to get data on traffic volume that matches the dataset I'm using. Unfortunately, I don't have that information, but we can look at other statistics to see whether these night incidents are more serious.

Of those incidents, 5.6% of incidents during the day had at least 1 fatality and 8.9% of night incidents had at least 1 fatality. Also, only 1.6% of incidents during the day had at least ten fatalities compared to 2.5% at night. This confirms that night incidents are slightly more likely to be fatal. It's also worth noting that among accidents reported as "dark night," 9.7% were fatal, showing only a slight increase from other night conditions. The percentage of total fatalities that happened at night is a bad statistic because a large amount of those fatalities come from a few large crashes.

Pie chart of incident statistics listed above

In a closely related statistic, 49% of the incidents during the day were not classified as "accidents," compared to 41% at night. This means the margin between an incident and a full-scale accident is narrower at night.

Some kinds of incidents are also far more common at night than during the day. 27.4% of incidents were marked as involving a weather condition at day versus 38.7% at night (which is surprising considering that thunderstorms and turbulence are less common at night). Other incident codes that represent a larger share of the incidents at night include "became lost or disoriented," "minimum descent altitude," "crew/group coordination," "airport facilities," "object," and, unsurprisingly, "light condition." Surprisingly, the following were not unusually common codes for night incidents: "terrain," "anti-ice," and "taxiway lighting" (wait what?). Some of these codes (like for taxiway lighting related incidents) are so rare that the statistics for them are unreliable.

I looked at the set of flights recorded by the NTSB since 1982 with light condition recorded and FAR part listed as 121, 125, 129, or "NUSC" (I make no guarantees that this dataset is an unbiased representation of all incidents since many crashes are excluded from these criteria). Dawn and dusk were considered during the day when counting. I'm counting by plane technically, not by incident.

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    $\begingroup$ Great research! May be worth noting, that the increase in night fatalities be simply because an injured person is harder to find in the dark. For example, someone exits the plane in shock, and wonders off away from responders instead of toward them, responders don't see the person because it's dark and they're focused on those they can see (until the passenger list is counted and they realize someone is missing). $\endgroup$ – FreeMan Jun 15 '16 at 12:56
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    $\begingroup$ For that matter, going to get groceries is probably more dangerous than flying no matter what time of day it is, assuming that you drive to and from the grocery store. $\endgroup$ – Sean May 28 '18 at 15:48
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There's not much statistical evidence to say conclusively. However, the FAA say that in general aviation 69% of crashes at night cause pilot fatality compared to 59% during day. Various FAA/NTSB reports state (f.ex: This) that there's more crashes during day than night but that's hard to interpret: There's a lot more planes in the air during the day.

For commercial aviation it's even harder to conclude anything. But this says that commercial aircraft fly around 1km closer to bad weather at night compared to during the day, which gives a rough indication that weather-related incidents may be more common at night.

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  • $\begingroup$ Answering your second paragraph, there may be more weather-related incidents at night, but it may just mean that pilots are over-cautious when they can see the weather coming. $\endgroup$ – Dan Hulme Jun 14 '16 at 14:07
  • $\begingroup$ Or it may mean that they're not cautious enough at night ;) Like I said, there's very little data one way or the other. $\endgroup$ – os1 Jun 14 '16 at 14:12
  • $\begingroup$ @sp1 I can't see 'not cautious enough.' Why would they be less cautious? More likely reliance on weather radar which can be tricky to use and can mislead pilots. $\endgroup$ – TomMcW Jun 14 '16 at 21:06
  • $\begingroup$ @TomMcW Human factors: If pilots see a storm out their window that looks scary then they'll often deviate by a larger margin than if they can only see it as a red blob on the radar. $\endgroup$ – os1 Jun 15 '16 at 6:28
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I don't know about statistics. Airliner crash stats are fraught with problems. The extreme rarity of the events means that any numbers suffer from small sample size.

Flying at night offers a lot of extra challenges compared to daytime.

Controlled flight into terrain (CFIT)

This is the accident category that is the biggest contributor to nighttime accidents. Many CFIT accidents occur in poor weather conditions (IMC) day and night, but there have been numerous incidents of CFIT in clear weather at night. The simple truth is, if they can see something they are far less likely to fly into it.

Weather

At night pilots have to rely on radar to avoid dangerous weather. Weather radar is not a simple thing to use. Pilots have to be trained how to use it effectively. But even in the best hands weather radar can still hide problems and be misleading. This is true during the day also, but the added ability to look out the window and see conditions can help pilots fly around storm systems.

I'm sure in some situations it would also be easier to see airframe icing during the day.

Spatial disorientation

This phenomena can be a real killer and even experienced pilots can succumb to it. It can occur during the day in IMC, but often at night, especially over open water, clear skies can be no help.

Optical illusions

There are some types of optical illusion that only occur at night. One example is the black hole effect

Pilot fatigue

Lack of sunlight is known to contribute to sleepiness.

Example accidents

Here is a short list of accidents that almost certainly wouldn't have happened during the daytime. These are just the ones I can think of off the top of my head, mostly ones I've seen on Mayday/Air Emergency/Air Disasters/Air Crash Investigation (I have no idea why that show has four different titles).

I can't really even think of a daytime crash that wouldn't have happened in the same conditions at night. Maybe Air New Zealand 901 that crashed into Mt. Erebus in Antarctica due to a daytime optical illusion.

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  • $\begingroup$ In case of CFIT, how could it be possible that a pilot crash a plane flying at 10Km above the earth to the ground by mistake? Doesn't he have the instrument to tell him the altitude? $\endgroup$ – MOON Jun 14 '16 at 23:21
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    $\begingroup$ In the AeroPeru accident they didn't have functioning instruments so they didn't know they were descending. The rest of the CFIT accidents happened on approach or just after takeoff. They either descended too low or got off course $\endgroup$ – TomMcW Jun 14 '16 at 23:25
  • $\begingroup$ This is a great list of accidents (especially the Mt. Erebus crash reference), but I'm not sure that all of these "certainly" would not have occurred during the day. Aeroperu 603, after all, wasn't the only crash due to altitude/airspeed confusion due to a blocked pitot tube. Perhaps saying it was a major contributing factor would be more accurate. That being said, aircraft can fly in zero visibility, but when the navigational aids they rely on fail, the blame isn't with the time of day- it's the problems with the navigational aids and the crew. $\endgroup$ – Cody P Jun 14 '16 at 23:39
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    $\begingroup$ @CodyP pitot failure crashes have all been either night or in imc $\endgroup$ – TomMcW Jun 14 '16 at 23:48
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    $\begingroup$ @CodyP Keep in mind, I'm not saying that night flying is unsafe. All IFR flights must be capable of flying in zero visibility down to their landing limits. I'm just saying that there are more challenges at night than during the day. $\endgroup$ – TomMcW Jun 14 '16 at 23:57

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