Airliner Flight Deck Question: What's with the orange and white balls?

[Caution Wake Turbulence]

Hello,

just watching this video:

and wondering what the contraption on the central windscreen pillar is for - the two orange and one white ball? Some sort of sight line reference point? Line up the white and orange balls and your head is in the ideal position?

Answers on a postcard...

Thanks,

Andrew

[Jessica]

It's a simple little parallax device to ensure that the pilot's seat is at the correct height for optimum visibility during landing. You adjust your seat height until the white ball covers the orange ball when you look at them.

[Caution Wake Turbulence]

Thanks Jessica. I wonder why only some 744s have them - KLM seem to like them.

Cheers,

Andrew

[MikeW]

I remember one of those NTSB documentaries into plane crashes, this exact thing was ultimately blamed for the PSA Boeing 727 that collided with a light plane over L.A. - the pilots had adjusted their seats to get comfortable which had then reduced the field of what was visible from the cockpit. The pilot of the Cessna was a trainee flying with a bag over his head basically, which made the whole thing seem doubly macabre.

[Jessica]

Caution Wake Turbulence, on 17 Nov 2015 - 06:01 AM, said:

Thanks Jessica. I wonder why only some 744s have them - KLM seem to like them.

Cheers,

Andrew

They're also standard equipment on Dash 8s.

[Caution Wake Turbulence]

Sure I've seen them on Airbus flight decks too.

Cheers,

Andrew

[Terrain Safe]

It's probably there so the pilot has the correct MEHT (minimum eye height over threshold) so that the pilots eyes are at the correct point with reference to the PAPIs.

[Jessica]

Terrain Safe, on 17 Nov 2015 - 1:13 PM, said:

It's probably there so the pilot has the correct MEHT (minimum eye height over threshold) so that the pilots eyes are at the correct point with reference to the PAPIs.

Well, at least so there's the best possible chance of it, given a properly executed glideslope. Not much any aid on the aircraft can do if you're 200 feet below or above where you're supposed to be.

Although given the choice I'd rather be above glideslope with the chance to go around. Mid-air collisions with planets are sooooo career-limiting.

[viscount806x]

Although given the choice I'd rather be above glideslope with the chance to go around.

You might then be the unlucky soul who landed long and disembarked the passengers onto buses direct from the far boundary overrun...

[noelh]

I remember one of those NTSB documentaries into plane crashes, this exact thing was ultimately blamed for the PSA Boeing 727 that collided with a light plane over L.A. - the pilots had adjusted their seats to get comfortable which had then reduced the field of what was visible from the cockpit. The pilot of the Cessna was a trainee flying with a bag over his head basically, which made the whole thing seem doubly macabre.

Not quite a bag but a hood or visor to prevent cheating while training for the instrument rating. The Instructor's job being to keep a good look out. But as they were hit from behind there was little they could do about that. Once I was berated by another pilot for cutting ahead of him during an approach. I politely pointed out that I was under the hood at the time and he should go and yell at my Instructor. Sometimes they actually cover the windscreen ahead of the pilot.

Like so many accidents the San Diego collision changed a lot of things.

[MikeW]

You are correct - it was San Diego. It was the AeroMexico DC-9 collision over L.A. One goes on a binge of watching those 'airline disaster documentaries' and some facts get muddled.

Cheers,

Mike

[Timo]

As I understand it, safety regulations mandate... installation of a fixed marker or other guide in transport aircraft to ensure that pilots adjust their seating position such that they are positioned at the ‘design eye reference point’.

The ‘eye height reference device’ in this 747 is the most common “fixed marker”. However, “other guides” include for example aircraft operating procedures that specify “3 line-of-sight references” as the accepted method for determining proper pilot seating position. Also flying with a HUD forces the pilot to sit in the correct position.

So some aircraft will have these devices, others won’t.

[Mark]

Yep, as mentioned earlier, the simplest device in the cockpit! Airbus definitely have them too.

[Skip]

As I understand it, safety regulations mandate... installation of a fixed marker or other guide in transport aircraft to ensure that pilots adjust their seating position such that they are positioned at the ‘design eye reference point’.

The "balls" do indeed define the Design Eye Point (DEP)(or Design Eye Reference Point) around which the cockpit is effectively designed. And the indicators do take different forms, Concorde for example had what could best be described as a lorgnette which had to be unstowed and mounted in position so of course was never used (as I suspect few if any of the others were either!). But the 3 balls set up was the most common and probably easiest to use. To be fair, the DEP is important, especially for low vis. operations or use of a HUD where field of view can be really important.

Skip

[Jessica]

Skip, on 18 Nov 2015 - 11:47 AM, said:

Design Eye Point (DEP)(or Design Eye Reference Point)

Given the internet, I can see why you skipped writing out the acronym for Design Eye Reference Point

Edited November 18, 2015 by Jessica

[Caution Wake Turbulence]

Having led a very sheltered life, I am of course going to have to google that right now...

I fear I may regret this.

Andrew

[viscount806x]

Yep, as mentioned earlier, the simplest device in the cockpit! Airbus definitely have them too.

Maybe not the simplest, did you ever use a bottle of water, held in front of the windscreen as a sighting horizon to see if you were going to overfly a distant cb or not? I picked that up from a very senior training captain and used it with good effect for many years. I expect there are other less techy things which might get a mention now....