How many altimeters does a big jet have ?

Question

I have heard that jet airliners have three altimeters. Is this true? If so, why do they need three?

Answer 1

HELLO

I DO NOT KNOW HOW MANY THEY HAVE BUT IF ONE FAILS MID FLIGHT THEY CAN'T LAND WITHOUT IT APART FROM GUESS WORK. WITH THE PRICE OF PLANES THAT SIZE IT IS FINANCIALLY ABLE TO CARRY AT LEAST ONE SPARE

ONE IN FRONT OF THE PILOT

ONE IN FRONT OF THE CO-PILOT

THIS BECAUSE WHEN NEEDED THEY BOTH FLY THE PLANE, THE OTHER IF THERE IS ONE COULD BY BEHIND THEM FOR THE FIRST OFFICER

Answer 2

only two are required unless the primary altimeters are on an EFIS display. then a third is required for back up. this accordingt to FARs 25, 125, 135, 121. the wild a$$ guesses just  keep on flowing in here.

Answer 3

There are three, Two primary which feed information to the pilot & co-pilot respectantly and the standby. If there is a difference in one then it is much easier to tell which one is wrong. The pilots always want redundancy in any primary instrument or control.

Answer 4

The captain has one on his computer screen, the co pilot has one on his computer screen and there is a back up old fashion one in the middle of the panel.

Answer 5

they need 3. L,R and C.

Answer 6

there are 3 one  for the capt one for the 1st officer then a standby altimeter.. the capt and 1st officers  work off of the air data computer and the standby works directly from the pitot-static system

Answer 7

Any airplane that can fly above 28,000 feet needs three altimeters.  This is a new requirement in the last few years because of reduced vertical spacing between usable altitudes.  It's so you can identify a false reading if there is one.  If there are only two altimeters and one gives you an erroneous reading, how do you tell which one it is?  If there are three and one gives an erroneous reading, you still have two functioning altimeters to identify which one is lying to you.

Answer 8

I have no idea.

Answer 9

Triple-x voting system.

If you get 3 values and one differs from the other 2, its more likely to be wrong.

If you only had 2 and they differed, you couldnt tell which one was right.