Aircraft instruments below sea level??

[Andrew P]

Heard that if a plane/helicopter is flying below sea level, e.g. Lake Eyre, the altimeter will not show any height?

Lake Eyre lies 10 metres below sea level.

Is this correct?

Banjo

[Mick F]

Incorrect. The altimeter still winds below 0ft when you change the QNH subscale, so can't think of any reason why it wouldn't show anything while flying.

Mick

[Will T]

As Mick said.

Pressure altimeters are 'dumb' instruments, and only show the sensed height above or below an arbitrary datum (being the QNH set by the pilot). As such, they certainly can indicate negative altitudes.

We regularly see the 744's altimeters in negative territory when the aeroplane has been sitting on the ground all day, and there has been a pressure change since the actual QNH was last set.

[Bill S]

I've seen about -10' plenty of times when I used to fly through Amsterdam.
They build jolly good dams, they do.

[Nigel C]

Does B!tching Betty scream to "pull up" before touchdown? Or were the B742's not equipped with her?

[Bill S]

Please refrain from quoting the whole post above in your post, it is not necessary - mod

That's a gadget connected to the radar altimeter, not the barometric one.
Your height above an arbrtrary datum isn't as important as one above a very solid one.