Sky pointer

[dcoded]

Can some one please explain why in commercial AC the sky pointer will point in the different direction.

I know that it has been like that for ages. But it really seems stupid.
In GA and military AC the pointer points in the correct direction.

There is an interesting small study regarding roll reversals with the commercial ADI.

In the study the conclusion is that the pilots in the test made 5 times more mistakes with the commercial setup, than the GA/mil setup.

Also there are speculations about some accidents caused by loss of spatial orientation.


But what I am wondering is why,even after we know that there has been accidents caused by the effects of the sky pointer, it is still used in commercial aviation.

What are your thoughts regarding this.
I have little or no experience regarding the commercial sky pointer other than some sim training and FS,hehe.

Edit: Here is the link to the study

http://www.leonardo.lth.se/fileadmin/lusa/Sidney_Dekker/articles/2003_and_before/Horizon.pdf

[sevenstrokeroll]

I understood that the sky pointer concept makes it easier to return to level flight.

and that is the most important thing...the recovery

after I got use to it, I loved it. but I did have to think for awhile, coming from a GA background.

[BOAC]

Once you have grasped the concept it is easy. In my (ex-mil/GA) experience it was not well stressed during airliner conversion and caused me significant confusion in the sim initially

[aviatorhi]

You're telling me people have bent metal because of a 1/4 inch black line on their ADIs?

Seems to me those people shouldn't have been near airplanes in the first place.

[dcoded]

Yes, there has been accidents because of this.

"I understood that the sky pointer concept makes it easier to return to level flight.

and that is the most important thing...the recovery"

Well if you read the findings you will see that this is not the case.
If you believe the report the recovery was 5 times WORSE with the commercial ADI. Here is a quote from the actual report

"While recovery on the military and General Aviation ADI was roughly similar, immediately
obvious was the inferior performance on the commercial ADI—ironically the ADI currently
used by all pilots tested. One pilot even made 100% roll reversal errors with the commercial ADI, and subsequent probing revealed that any misunderstanding was not the reason for his
performance."

Also
"Discussion

Roll reversal errors on the commercial ADI were almost 5 times more frequent than on the other two ADI's. Since there were no significant differences in response latency across the three different ADI presentations, pilots do not appear to engage in a speed-accuracy trade-off (cf.Gardner, 1954). That is, the much higher probability of roll reversal on the commercial ADI's
is not preceded by a faster response time when faced with a commercial ADI presentation, which means the higher error rate stems from other sources. This large performance gradient, by pilots who actually use the commercial ADI in their daily practice, would point to the importance of the control-display compatibility principle in using the roll index for directing
recovery action. Indeed, this result mimics the findings by Kovalenko (1991), that no amount of overlearning (all pilots tested in our study had a minimum of five years commercial ADI experience) can likely overcome the inherent incompatibility between required control action and display movement in the commercial ADI."

I find this very interesting. I can recommend that you read the report. It's not so long.

[PEI_3721]

Often misinterpretations of instrument display represent differing views between design and operational use. Additionally, differences in how pilots have been taught to use the instrument or the meaning of specific indications for special situations.

If the inference is that a commercial sky pointer is used to recover roll attitude, I offer a different view, in that the primary roll reference is the horizon. Furthermore, a sky pointer should be used against its own reference (not the sky), in some cases this could be considered to be the aircraft fin – the fixed reference on the outside of the instrument – which is part of the aircraft.

Thus without the details of the ‘experiment’ – pilot experience, beliefs about system operation, or the task, then the results can be used out of context.
The objective of the report (Singer / Dekker) appears to seek further understanding of the Saab 340 accident involving LOC after takeoff and during a departure turn. IIRC the official report cited East/West differences in display type against the pilot’s experience (East) as a contributory cause. This problem as I understand, is between ‘inside’ and ‘outside’ types of displays and not specifically about sky pointers.
Also, IIRC the Saab 340 was one of the first aircraft with EFIS which used a full screen display of attitude vs a containing instrument. I found that at larger bank angles this type of display had some distracting features when the horizon transitioned from the side edge of the EFIS to the top/bottom edge.

[411A]

In GA and military AC the pointer points in the correct direction.


Oh dear, here we go again.
IF you look in nearly any GA airplane in the USA (where GA airplanes outnumber nearly all other countries, combined), you are quite unlikely to find a 'ground pointer'...only a sky pointer, to indicate bank angle.

That 'ground pointer' baloney is utter nonsense...and as we might suspect, it generally originates from... the land where refrigerators were recently discovered...the UK.:rolleyes:

[Sunshine Express]

Errrr......what?

Anyway, I know exactly what you mean regarding the sky pointer. It seems odd transferring from light or military aircraft but somehow one just becomes accustomed to it. Best not to think about it too hard and it seems logical.


P.S. I had a look at 411A's public profile and it states: "411A has not made any friends yet"

Soooooo true! :)

I expect mine says the same though, although probably "-1" now!

Off to put a new block of ice in my new fangled refrigerator thingy...:rolleyes:

[boofhead]

You are missing the point of the pointer reference.
High performance airplanes have a different display of roll reference when using the sky pointer. I have noticed that the Collins 108 fitted to the King Air has a different method of displaying roll (I need to fly the airplane again to be able to describe it). I think it is the way the tape on top of the instrument moves which makes the relevant difference between the sky pointer and the "sky" work in the opposite direction. I cannot remember the details, the King Air has been down for engine change for three months and I have not flown it for a while, but I remember it always made me pause the first time I flew it after most of my time was on smaller piston types. I asked someone why they were different and was told it was because there were GA displays and "jet" displays.
I suspect the King Air has an airline type display while the smaller GA airplanes have a more basic system.
I hope to fly it later this month and will take a closer look.

I did get a chance to look at two different attitude indicators. One was the Collins 108 similar to those fitted to the old B737 and to the King Air, the other was a normal GA AI. The Collins was different in that the bank scale at the top is fixed, thus it moves with the airplane. The sky pointer always points vertically. The GA instrument has a moving scale and the sky pointer is fixed with the airplane. This shows the apparent movement of the sky pointer in opposite directions for the same bank angle. It takes only a little time to become used to the differences, but it is nevertheless different.

[a.maruskins]

The main idea to make AI with the sky pointer moving opposite direction of the turn is to follow the same idea in all the indicators design. All the instruments are displaying the deviation of the profile required. The same is for the pointer - it is displaying the deviation of the level flight. i.e. which direction a pilot should follow to come back to level flight.

The construction of the AI with the sky pointer moved in the direction of the bank is easier, as also cheaper. This is why they are more popular I think. But if you would analyze instruments on a new Glass Cockpit GA aircrafts you will see the same "commercial aircraft" AI display on Cessna as also on B738.

If you want be never confused by the information indicated you should never use your GA instrument reading experience flying a commercial aircraft. It is very simple in reality.