Normally when an aircraft departs, the landing gear is retracted shortly after the aircraft is airborne. While watching aircraft departing from an airport in my city, I noticed, that occasionally the pilots leave landing gear down for many miles (10NM or possibly more). What is the reason for this, are they trying to cool down something?
$\begingroup$ Is it the same type or aircraft each time you see this, if you're able to tell? Also, have you ever observed them first retracting the gear and then, after gaining some altitude, lowering it again for awhile? $\endgroup$– TerryAug 29, 2018 at 22:17
$\begingroup$ I saw this happen twice, in both cases they were A333 from two different airliners. The gear was left open since the a/c got airborne, and both aircraft continued with the departure as per normal SID. $\endgroup$– krisAug 29, 2018 at 22:59
$\begingroup$ Correction to my previous comment: it was A333, and then B788. $\endgroup$– krisAug 29, 2018 at 23:06
$\begingroup$ Location information could provide a hint. Is it a hot place ? $\endgroup$– kebsSep 9, 2018 at 7:42
$\begingroup$ Kebs: location Sydney, Australia, during winter (around 17*C during the day) $\endgroup$– krisSep 10, 2018 at 10:23
It's usually for one of two reasons:
Brake temps are displayed in the cockpit and if the temps were elevated from a lot of, or excessive, brake use during taxiing, the capt may delay retraction until the indications come down, mainly to avoid gear bay overheat indications. This will be more common on airplanes that have more idle thrust than necessary to roll at normal taxi speed, which can cause a tendency to ride the brakes. CRJ200s, which can get going pretty fast on idle thrust with both engines running, are really bad for this.
Also in winter on a departure from a slushy runway, retraction may be delayed to try to blow off as much slush as possible since once the slush freezes, it can immobilize the wheels, preventing normal spinup on the next landing (if it's still cold at destination).
$\begingroup$ Some Airbus aircraft (e.g. A320, A330) do not have wheel well fire/overheat detection. Instead, the BRAKES HOT ECAM procedure requires that they re-extend the gear until the brakes cool below the ignition temperature of leaking hydraulic fluid. (This answers the OP's comment that they saw it on A333s) $\endgroup$ Mar 16 at 18:10
It could be that the Wheel Well Fire Detection System was inoperative.
According to the B-787 "Master Minimum Equipment List" (as shown from this website, in pertinent part) the Wheel Well Fire Detection System:
"May be inoperative provided landing gear remain extended for ten minutes after takeoff."
Cooling the gear after takeoff is one likely scenario, if the aircraft had only a short time on ground between landing and takeoff. Another scenario (from memory - standing by to be corrected) is an inoperative wheel brake on one of the main gear wheels, where sufficient time must be allowed after takeoff to ensure the wheel is spun down before retraction.