Eye Height Reference Device - Boeing 737

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Hello All:

FAR 25.773 (d) mandates installation of a 'fixed marker or other guide' in transport category aircraft to ensure that the pilots adjust their seating position such that they are positioned at the design eye reference point.

Looking at pictures of 737-500 flight compartments, I cannot see any evidence of an 'occluded sphere' type reference device installed on the windshield center post. Did Boeing use a different type of 'fixed marker or other guide' on these early 737s to comply with this FAR, and if so, what methodology did they use? Or, were these aircraft built to a certification basis that preceded publication of FAR 25.773 (d)?

Many thanks in advance for any light that an expert could shed on this question.

(Question was originally posted in the 'Flight Test' forum, but received no response there.)

[Boingboingdriver]

HI,
I believe looking in your aircraft systems manual,in the section #pilot seat adjustment#you may just find the answer.could tell u but too lazy.

OK change of mind...pilots hould sit in order to see the top glareshield and the bottom of the outboard display....then its up to you in flight to readjust this to feel comfy....

Capt STD:E

[AirRabbit]

Looking at pictures of 737-500 flight compartments, I cannot see any evidence of an 'occluded sphere' type reference device installed on the windshield center post. Did Boeing use a different type of 'fixed marker or other guide' on these early 737s to comply with this FAR, and if so, what methodology did they use? Or, were these aircraft built to a certification basis that preceded publication of FAR 25.773 (d)?
Many thanks in advance for any light that an expert could shed on this question.

Well, there are probably several reasons for this … first, the B-737-300 was the first design to follow-on behind the B-737-200 Advanced model and the B-737-400 was the “larger version” of the -300, and the B-737-500 was the “smaller version” of the -300. Initially, there well may have been some sort of alignment indicators installed in the -300 that occluded one another with the pilot’s eye position properly placed. However, when follow-on models of essentially the same aircraft were developed and placed into service, a quick review of this proper eye position could be verified by, 1) being able to sight directly down the top of the glare shield; 2) able to clearly see the top annunciator lights above the flight instruments; and 3) able to see the bottom of the Electronic Horizontal Situation Indicator (EHSI). If this turned out to be accurate, there just may be little need to install (and maintain) the occuluding sphere references. If you check the flight crew operating manuals for the B-737-500, I think you’ll find this “3-line-of-sight-references” included as the method accepted for determining proper pilot seating position in the -500 series aircraft.

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...I believe looking in your aircraft systems manual...

...If you check the flight crew operating manuals...

I'm sorry, perhaps I should have made it clear that I don't fly a Boeing aircraft, never have and probably never will. I'm an engineering test pilot for a different type of aircraft. I specified an eye height reference device be installed in one of the aircraft I am responsible for, and one of my co-workers (who flies a 737-500) mentioned that the Boeing didn't have one. I looked at various pictures of 737-500 flight compartments and sure enough, there is no occluded sphere EHRD there.

So - in light of the fact that I have neither an actual 737-500 or a FCOM for a 737-500 handy - can anyone tell me if there is 'fixed marker or other guide' (the exact wording of the applicable FAR) installed in 737-500s to enable the pilots to ensure that they have positioned themselves at the DERP?

AirRabbit has explained that one can adjust seating appropriately by making three reference checks, and this makes a lot of sense, but does this fulfill the requirement for the 'fixed marker or other guide'?

Many thanks in advance to anyone who can tell me if there is a physical 'fixed marker or other guide' in the 737-500.

[c100driver]

Yes it meets the requirement of "other guide". The last B737 that had the ball guide I have flown was a B737QC-200ADV circa 1981, we had some later model B737 200ADV new from the factory and they did not have the balls fitted.

Our B737-300 aircraft were delivered from the last batch of CL B737 (1998/9) Boeing built and none of those had the ball either.

From a trainer point of view, if you position to the exact sighting picture as per the FCTM then you will be set at the same eye height.

[AirRabbit]

AirRabbit has explained that one can adjust seating appropriately by making three reference checks, and this makes a lot of sense, but does this fulfill the requirement for the 'fixed marker or other guide'?

In a word, Yes. The FAR requirement allows for either the “fixed marker” or “other guide.” The point is to allow the pilot to achieve the proper eye reference position in 3-dimensional space. Because most pilot seats do not have side-to-side adjustments except at the most aft position (for ingress/egress ease – and then the requirement is usually to have the seat in the forward “X” inches of travel – to prevent side-to-side errors), the only two adjustments that remain are “fore/aft” and “up/down." If you use the technique of sighting down the top of the glare shield, while being able to see the top of the annunciator lights above the flight instruments; AND are able to see the bottom of the EHSI, you will have achieved the necessary “fore/aft” and “up/down” positioning that would place your eye reference in the prescribed location.

[Tankengine]

If flying an NG with a HUD then you are forced to sit in the correct position!:ok:

[FullWings]

I've tried using the recommended seat positions on several types of Boeing, using exactly the procedures in the manuals and have always ended up in a posture where flying is almost impossible.

I have found that if a) I have a line of sight down the coaming and over the nose, b) the instruments are visible and c) I can get full control movement without hitting myself, then I have a good chance of taking off and landing without too many issues. Observing people I fly with, there is much variation in how they sit, so there's probably quite a large optimum band.

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Hello AirRabbit:

Thanks very much for the complete and comprehensive answer. I was truly puzzled by the lack of a traditional 'occluded sphere' device, but after having read your response, everything now makes sense.

[Mr.Buzzy]

How is adjusting your seat in a plane any different to adjusting your seat in a car?
If you're comfy...... you're comfy. Just twiddle the levers until you can see and reach everything.... Hardly a moonshot.

bbbbbbbbzzzzzzzzzzzzbbbbbbbzzzzzzzzzzzzzzzzz

[AirRabbit]

Hello AirRabbit:
Thanks very much for the complete and comprehensive answer. I was truly puzzled by the lack of a traditional 'occluded sphere' device, but after having read your response, everything now makes sense.
My pleasure. Glad to have been of service!

How is adjusting your seat in a plane any different to adjusting your seat in a car?
If you're comfy...... you're comfy. Just twiddle the levers until you can see and reach everything.
Well, if you can't tell the difference between your seat in your car and your seat in your airplane, it probably makes no difference at all. So...let us know how your lunar landing goes...