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Night Flights: Newsletter Challenge (September 2019)

Posted August 31, 2019 5:01 PM
Pathfinder Tags: airport challenge question

This month's IEEE GlobalSpec newsletter challenge is:

While trying to book a flight to Qamdo Bamda Airport in Tibet, you're frustrated to find that all the flights take off and land at night. Why does the airport engage in this practice?

And the answer is:

The airport’s policy is most likely a restriction to ensure safer conditions for takeoff and landing.

At high altitude, air density is lower. Air density also decreases as temperature rises. The combination of a hot day and high altitude results in low air density that reduces aircraft engine power. At night, when temperatures are lower, the air density is a little higher, so engines can produce a little more power.

Low air density and low engine power mean the aircraft will produce less thrust and lift. For takeoff at high altitude airports, aircraft need to reach a higher speed before sufficient lift is generated compared to sea level airports. They also land at higher speed for the same reason. As a result, a longer runway is required at high altitude airports to give aircraft the time to reach the necessary takeoff speed (and time to slow down after landing). Rate of climb after takeoff is also reduced, which could be dangerous if the aircraft needs to gain altitude quickly to clear mountain tops.

As such, Qamdo Bamda Airport has the longest publicly used runway in the world, 18,045 ft (3.41 miles) long. Typical commercial airport runways are between 8,000 ft (1.5 miles) and 13,000 ft (2.46 miles) in length. It is also the second highest airport in the world at 14,436 ft elevation.

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#1

Re: Night Flights: Newsletter Challenge (September 2019)

08/31/2019 7:44 PM

Probably would have to do with wind speed, at an altitude of 14.4k ft the weather is unpredictable and the average wind speed is like 30mph...at night the wind probably dies down a bit...

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#2

Re: Night Flights: Newsletter Challenge (September 2019)

08/31/2019 9:06 PM

Qamdo Airport was formerly the highest airport in the world, therefore air density is low, resulting in an extra long runway for take off, therefore I suggest that the night time air temperature is cooler than the day time resulting in a more efficent thrust from the engines?

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#3
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Re: Night Flights: Newsletter Challenge (September 2019)

08/31/2019 9:42 PM

Agreed. The pressure altitude is lower with lower temperatures (denser air) at night. It affects not only the engines but the performance of the wings. In the daytime, not only are the engines weaker but the planes need to go faster to get off the ground and can carry less payload.

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#4
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Re: Night Flights: Newsletter Challenge (September 2019)

09/01/2019 10:31 PM

We usually referred to density altitude when planning departure time from high altitude airstrips, e.g., summertime at Bryce Canyon comes to mind <https://www.experimentalaircraft.info/flight-planning/aircraft-performance-3.php>.

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Re: Night Flights: Newsletter Challenge (September 2019)

09/02/2019 11:25 PM

Agreed, that has raised another point in my mind, are night time departures necessary to match day time landings, as some airports are only day time arrivals only?

But, I agree with the two points you raised, engine and wing performance, I think covers it. GA.

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#5

Re: Night Flights: Newsletter Challenge (September 2019)

09/01/2019 10:36 PM

Given the elevation it is safe to assume that there is a bright white snow cover 24/7/365. Combined with the ultra-long runway snow blindness for the pilots is a constant daily concern.

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#6
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Re: Night Flights: Newsletter Challenge (September 2019)

09/02/2019 2:25 AM

Definitely not snow-covered 24/7/365
It is the last remaining habitat of the extremely rare Tibetan Echidna Platypus which as a nocturnal predatory carnivore only mates and sleeps during the daylight hours - hence the night time flight regime which goes some way to protecting the peasants from these fierce creatures.
The fact that the aircraft work better then is a wonderful side effect/benefit.

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Re: Night Flights: Newsletter Challenge (September 2019)

09/02/2019 9:23 AM

artistic rendition....

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#8

Re: Night Flights: Newsletter Challenge (September 2019)

09/02/2019 4:14 PM

The Chinese military might see you during the day .

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#9

Re: Night Flights: Newsletter Challenge (September 2019)

09/02/2019 4:53 PM

You're all wrong, I happen to know this is where all the vampires live, they can only travel at night...

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#11

Re: Night Flights: Newsletter Challenge (September 2019)

09/03/2019 6:40 AM

Because they use Bejing time. (Air is densest early in the morning & all their arrivals/departures are between 7am & 11 am local time)

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#12

Re: Night Flights: Newsletter Challenge (September 2019)

09/03/2019 8:19 AM

Corollary question: Does the size of the airplane affect the time of day the plane can take off? Can a smaller commercial jet -- like those that regional airlines use in the US -- take off during daylight when larger long-haul planes cannot?

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#13
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Re: Night Flights: Newsletter Challenge (September 2019)

09/03/2019 1:15 PM

I had to do some extra calculations flying a Piper Cherokee 180D out of Bryce Canyon airport one summer day--If I had just one other person on board (or more fuel) I'd have to delay takeoff until after sundown when it was cooler. As it was the takeoff roll seemed to go forever.

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Re: Night Flights: Newsletter Challenge (September 2019)

09/03/2019 8:07 PM

Good question.

"A runway of at least 6,000 ft (1,829 m) in length is usually adequate for aircraft weights below approximately 200,000 lb (90,718 kg). Larger aircraft including widebodies will usually require at least 8,000 ft (2,438 m) at sea level and somewhat more at higher altitude airports. International widebody flights, which carry substantial amounts of fuel and are therefore heavier, may also have landing requirements of 10,000 ft (3,048 m) or more and takeoff requirements of 13,000 ft (3,962 m). The Boeing 747 is considered to have the longest takeoff distance of the more common aircraft types and has set the standard for runway lengths of larger international airports."

https://en.wikipedia.org/wiki/Runway#Runway_length

The required runway length for an aircraft type is a factor of both density altitude and takeoff weight. (Airlines make more money if their planes are loaded.)

Here is a plot for the "infamous" 737-800

http://128.173.204.63/courses/cee4674/cee4674_pub/acft_run_length.pdf

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#15

Re: Night Flights: Newsletter Challenge (September 2019)

09/05/2019 1:46 PM

There is no Qamdo Bamba Airport in Tibet...or anyplace else....

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#16
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Re: Night Flights: Newsletter Challenge (September 2019)

09/05/2019 2:01 PM

Correct -- fixed the spelling in the question.

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#17

Re: Night Flights: Newsletter Challenge (September 2019)

09/11/2019 12:36 PM

Answer is posted.

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