What is the purpose of this loop in a taxiway?

This image is of Mariscal Sucre International Airport near Quito, Ecuador. (Official site / in English)

What is the purpose of the loop in the taxiway plainly visible in this image?

From Google Earth (with the contrast punched up a bit)

To respond to the comments to jwzumwalt's answer, I really don't think the hills and mountains to the north of this airport are an operational concern. See below image:

Source plus my copy-and-paste extras

The airport's elevation is 7900 feet (verified by Skyvector), the first ridge in jwzumwalt's 2nd image is 6.4 miles distant from the north end of the runway and lower in elevation, and the second ridge is 8 miles distant but only 500 feet higher. Distances verified by Google Maps.

If an aircraft can't comfortably clear a ridge 500 ft above the airfield in eight miles, well then that's a whole other issue. :-)

But, I do like jwzumwalt's answer. Thanks!

• After seeing your data, I admit the Google map was deceiving me. However, the peak just to the right of your "8,432" is "9167 ft". That's a difference of 1270ft + obstructions (if it has towers might be ~2500ft). At that altitude on a hot humid day many aircraft would not be able to climb above. At 25C (77F) a C-172 has 200fpm climb which coincidentally at 80mph/~120fps a C-172 will climb 200ft per mile and wouldn't clear tall obstructions along it's path. Commented Jun 15, 2018 at 21:17
• I sent the following message to the airport using their website: I'm hoping you can provide a definitive answer to the question on aviation.stackexchange.com concerning the use of the loop in the taxiway at the north end of the runway off the west side. The url to see the question and guesses so far is aviation.stackexchange.com/questions/52663/…. My guess is that it is to facilitate aircraft movement when using rwy 18 for takeoff and 36 for arrival. Commented Jun 18, 2018 at 16:32

In the US, this is called a "run up area". It is used by small piston powered airplanes to test their engine prior to takeoff.

The circular design allows several aircraft to full throttle their engines without the prop blast hitting the aircraft behind it. It also allows other aircraft like a business jet, to pass the testing aircraft and takeoff immediately.

Larger aircraft or turbine powered aircraft don't usually test their engines near taxi-ways and other aircraft (or aren't allowed). If they need to test their engines, a special blast "pen" or blast "barrier" is used.

Youtube video of a FedEx engine test.

This Youtube video of a airplane landing shows a ground view of the significance of the hills and mountains off the departure end of 36.

Why the run-up is at this end - Google Earth 3D

• Thank you for the answer, but I'm still curious, how come this run-up area is at the opposite end of the take-off runway usually used at UIO? Or is that the normal procedure / location? (I don't have wind rose data, but suffice it to say that at UIO, nearly always T/O and landings are to the north.) Commented Jun 15, 2018 at 10:09
• Aircraft use either end of a runway depending on wind direction. The Mariscal Sucre runway has high speed exits in both directions showing it is used in both directions. However, due to hills to the North, it appears landings are normally from the South and takeoffs are from the North end. Commented Jun 15, 2018 at 12:19
• @jwzumwalt: Umm, every time I've been to that airport, day or night, all operations are on Runway 36. As for the hills, well check out youtu.be/7G0lTmezE_Q. Disclosure: I recorded that video. Commented Jun 15, 2018 at 15:24
• @pr1268 You're correct on that, the Ecuadorean AIP says that 36 is used for all takeoffs and landings, except when the wind is from the south at 8kts or more, then 18 can be used. 36 departures may not turn right, and 18 departures may not turn left, so I guess the terrain east of the airport is the main operational issue. There's nothing specific that I can see in the AIP about taxiway T, by the way. Commented Jun 15, 2018 at 15:33
• Here's the exception to the rule: A landing on Runway 18. youtu.be/qCVmDIT4qEA Commented Jun 16, 2018 at 10:19

Also looking at the layout of the airport, it gives planes a holding area in case they need more time to get ready. If there was traffic behind them they would have to taxi down the runway until the mid-point and then back up the taxiway Quito is a high airport with some long haul flights.. take-off performance may be restricted and this may result in the plane being a bit overweight so this may be an area to allow for airplanes to burn-off some fuel. As an example the aircraft may have a restricted take-off weight of 280,000kgs. A forecast ZFW (weight without fuel or zero fuel weight) of 200,000kgs may be given to the crew. The crew may then decide to uplift 80,000kgs of fuel which would bring the take-off weight up to the allowed 280,000kgs. However as the forecast ZFW was only a forecast.. the actual ZFW may exceed due to last-minute passengers, cargo, baggage etc. If it is a big amount (more than 2-3000kgs) they would probably offload some cargo but if it was only 1,000kgs or so the crew may elect to burn off some fuel to get the legal weight before taking off.