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CNN's September 17, 2024 This airport landing is so challenging only 50 pilots are qualified to do it is about

...Bhutan’s Paro International Airport (PBH), widely considered one of the most technically difficult plane landings in the world. Maneuvering onto a short runway between two 18,000-foot peaks requires both technical knowledge and nerves of steel.

The article goes on, quoting "...Captain Chimi Dorji, who has been working at Bhutan’s national state-owned airline, Druk Air (aka Royal Bhutan Airlines), for 25 years."

“In Paro, you really need to have the local skills and local knowledge area competence. We call it area competence training or area training or route training from flying from anywhere into Paro,” he tells CNN Travel.

Bhutan, which is located between China and India, is more than 97% mountains. Its capital, Thimpu, is 7,710 feet (2,350 meters) above sea level. Paro is slightly lower, clocking in at 7,382 feet.

“At higher elevations, the air is thinner, so the aircraft essentially has to fly through the air faster,” explains Dorji, who in addition to flying planes now trains Druk Air’s pilots and cabin crew. “Your true airspeed will be the same, but your airspeed as opposed to the ground is much faster.”

I don't understand the last sentence - what's the difference between "true airspeed" and "airspeed as opposed to the ground", and why would the latter be "much faster"?

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    $\begingroup$ And instead of "airspeed as opposed to the ground" we usually say "ground speed." $\endgroup$
    – randomhead
    Commented Sep 17 at 15:12
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    $\begingroup$ Looks like a bad translation or transcription of what the Captain probably said. Something like “Your indicated airspeed will be the same, but your speed over the the ground is much faster.” $\endgroup$
    – Ralph J ♦
    Commented Sep 17 at 18:45
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    $\begingroup$ Sounds like the Captain was trying to dumb-down a slightly tricky couple of concepts, in a language that is not his own, and did a pretty good job of it, if we isolate a couple of bits: "the aircraft ... has to fly through the air faster" & "your [air]speed as opposed to the ground is much faster." So: stall-speed is higher; landing speed is higher > ground speed is higher on touch-down. $\endgroup$
    – MikeB
    Commented Sep 18 at 12:52
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    $\begingroup$ something occasionally noted is the simplification of an explanation for ease of understanding by the general public... $\endgroup$
    – Thomas Perry
    Commented Sep 20 at 23:26

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The statement as given does not make much sense. The use of the term "airspeed as opposed to the ground" already indicates that imprecise terminology is being used here. This is called ground speed and is (as the name suggests) not an airspeed.

In general, aircraft take off and land at a given calibrated airspeed (which depends on weight and flap configuration). The true airspeed corresponding to this given calibrated airspeed will increase with altitude because the air is less dense. I think this is what pilot meant to say. This true airspeed is also equal to ground speed if there is no wind.

According to the article, Paro airport is at 7,382 ft AMSL. For standard atmospheric conditions, this means an calibrated airspeed of 150 kt will correspond to a true airspeed of ~167 kt (see e.g. aerotoolbox.com), an increase of ~11%. Note however that kinetic energy scales with velocity squared and is therefore increased by ~24%, resulting in significantly longer takeoff and landing rolls.

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  • $\begingroup$ Thanks! OK so for whatever reason (mistranslation, mistranscription, misquote, editor's intervention, etc.) "Your true airspeed will be the same" is not right, but as RalphJ suggests "“Your indicated airspeed will be the same" would fix the 1st half, and "your ground speed would be (about) the same." would fix the 2nd half? Have I got the basic idea correct? $\endgroup$
    – uhoh
    Commented Sep 18 at 5:55
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    $\begingroup$ Yes, I agree that the first one should say indicated or calibrated instead of true airspeed (we usually use calibrated airspeed on an airliner). The second one should be "ground speed is much faster" (not the same). $\endgroup$
    – Bianfable
    Commented Sep 18 at 5:59
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Without entering into the details about the differences between indicated airspeed, equivalent airspeed, true airspeed or calibrated airspeed (and for sure I'm forgetting some other airspeed), what the interviewed pilot wanted to say (possibly not with the right wording) is simply that, being lift proportional to the product $\rho V^2$, if you're landing at higher altitude (i.e. lower density $\rho$) then you have to compensate for it by increasing $V$. Being a mountainous place, gusts mitigation might also dictate a further increase in the landing speed. As simple as that.

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