Can anyone explain what might be going on in the last hour of this flight while they circled LHR? Why would the speed fluctuate from 180kts to 300kts every 4 minutes. For an hour!
Most likely poor speed reporting in the turns of that hold. It dips in the turn and spikes in the legs of the hold.
Isn’t that the real speed thou?
The air speed in a turn, with the plane banked, has to be higher in order to maintain the same altitude like in straight flight legs.
Thanks guys. Another theory I heard is there was a strong prevailing wind at the time. But the wind would have needed to be 60ish knots, right? I suppose that’s possible at 10000 feet.
The oscillations continue down to around 5000 feet, at which point perhaps he lined up for final and they stopped.
Although drag increases in a turn, power would be added and pitch adjusted to maintain the flight path. So actual airspeed would remain constant. Ground speed would vary between the into wind and down wind legs, but not airspeed (apart from minor fluctuations). Currently an unexceptional weather situation over southern England, but there are 40 kt winds at 10,000’ in some areas.
Reviewing the flight info shows that the indicated airspeed sits at around 220kts with minor variations.