momentarily

A friend has just e-mailed me that just as her plane was taking off from Chicago airport the pilot announced to the passengers: we will be airborne momentarily. We don't think he was expressing a lack of confidence in his aircraft, which is what the phrase would imply in BE, but that they would shortly be airborne.

I suppose this must be standard usage in AE, or a pilot wouldn't risk causing panic amongst the passengers. Am I right?

Yes, it is. I understand it both ways, as meaning IN a short time and FOR a short time. So I would immediately understand the pilot to mean IN a short time, but I would also say, "He was momentarily at a loss for words", meaning FOR a short time.

BTW, I think it's possible (though I'm not sure about this) that the position in the sentence tells me which definition is intended. If the pilot had said, "We will be momentarily airborne," I DEFINITELY would have panicked, right along with all the Brits on the plane.

Thomas Tompion said:

A friend has just e-mailed me that just as her plane was taking off from Chicago airport the pilot announced to the passengers: we will be airborne momentarily. We don't think he was expressing a lack of confidence in his aircraft, which is what the phrase would imply in BE, but that they would shortly be airborne.

I suppose this must be standard usage in AE, or a pilot wouldn't risk causing panic amongst the passengers. Am I right?

This seems to be a standard announcement by US flight attendants.

The first time I heard it, I was surprised. I've got used to it, and added it to the list of AE v BE differences.

It used to mean 'for a moment' in AE, too, but now it means 'in a moment' just as often (maybe even more often). The author of one popular AE usage manual blames airline pilots for this change.

Momentarily with the AE meaning predates airline pilot announcements somewhat. Here are the earliest examples from the OED:
1869 A. J. WILSON Vashti xi. 149 Robert is bringing her home as carefully as possible, and you may expect them momentarily. 1928 Sun (Baltimore) 13 Aug. 1/2 Arrests were expected momentarily as police continued their investigation.