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I was on board flight NU 54 (Japan Transocean Air / B737-800) November 1st. Looking at the sea surface, I had the impression that the plane flew low for a long time before climbing, which is confirmed by the following flight data: https://fr.flightaware.com/live/flight/ ... F/tracklog

That is nearly 3 minutes at less than 500m altitude, or nearly 5 minutes at less than 1000m. Is this an unusual take-off? I think so, because most other flights on the same route reach 500m altitude in around 30 seconds and 1000m altitude in less than 2 minutes.

The objective here was, I think, to find an area where the cloud cover was less dense to climb (the weather was bad). But how long can an airliner continue to fly at low altitude before climbing? Isn't there a danger to fly for a long time at less than 1000m? Thanks for your feedback!

There is no danger as long as there are no terrain clearance issues.

The only significant consideration is higher fuel burn at lower altitude, but a few minutes won't make a difference.

The typical reason to be kept low is for traffic.

I'm not a pilot, I only play simulators, but one of the northbound standard departures at Naha keeps you at around 1000ft for quite a while. I suspect it's to keep clearance with arrivals at Kadena Air Base.

You really have to keep in mind the overall picture. As Starlionblue said, traffic may be a factor - including traffic off Kadena Air Base up the coast. Low clouds are not going to be an issue for IFR aircraft, unless those also come with convection.

PepperTaco wrote:

I'm not a pilot, I only play simulators, but one of the northbound standard departures at Naha keeps you at around 1000ft for quite a while. I suspect it's to keep clearance with arrivals at Kadena Air Base.

This sounds like the sensible reason. The runway direction at Naha is essentially north/south and Kadena is east/west. The departure and arrivals for Naha tend to fly under the Kadena flight path.

You did not specify the airport you had departed from. I've operated from Naha and the departure required climb only to 1000' until cleared by ATC. This is normal at that airport. There are other airports that have departures level at other levels (below 3000) for a segment often involving a turn. Of course, if a problem is encountered in the initial climb, the crew might elect to level off and initiate abnormal or emergency profile and procedures.