Va - Maneuvering Speed- What's It Mean to You
- Thread starter Firebird2XC
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Divine Wind
New Member
A fact not many pilots knew prior to AA 587, including myself. Most pilots familiar with stall recovery and aerobatics know the rudder is more effective at slow speeds than the ailerons. Couple this knowledge with a misinterpretation of a company manual (AAMP), lack of training in wake turbulence recovery techniques and it is an accident waiting to happen.
From the NTSB accident report pg 12:
Like many NTSB reports, they are very good reading for learning from the mistakes of others. Rarely does the fault of an accident squarely and singularly belong on the shoulders of a pilot. According the Reason model of accident causation (aka Swiss Cheese model) the pilot is almost always the last obstacle to an accident but it is never alone.
phoenix 23684
Well-Known Member
Here's my take on Va, the speed at which you can apply full up elevator and not cause any damage. Doesn't work the other way around, lets say you apply full nose down, most likely will exceed manufacturers negative G loading and regret it. That's it nothing to do with ailerons/rudder deflection.
Why do I say that, well, the slower you go the higher and closer your AOA to MAX AOA, Va should guaranteed that when you apply all this up force. i.e. sudden increase in AOA, you will reach max AOA before reaching max positive G load, get airflow separation and induce a stall preventing you from overloading the wings, but going the other way you have nothing protecting you from reaching a max negative load.
This is why Va changes with weight, has little to do with inertia, as some people are missed instructed, and more to do with AOA. A heavier airplane requirers a higher AOA to sustain level flight. So let's say that your wing reaches Max AOA at 15 degrees, and lets say Va puts the wings at 10 degrees AOA giving you a 5 degree cushion. Then a lighter airplane needs to go slower to get an AOA of 10 degrees and a heavier airplane can go faster while maintaining that same AOA.
Now it has been a few years since my AE degree and a few as well since CFIing.
Why do I say that, well, the slower you go the higher and closer your AOA to MAX AOA, Va should guaranteed that when you apply all this up force. i.e. sudden increase in AOA, you will reach max AOA before reaching max positive G load, get airflow separation and induce a stall preventing you from overloading the wings, but going the other way you have nothing protecting you from reaching a max negative load.
This is why Va changes with weight, has little to do with inertia, as some people are missed instructed, and more to do with AOA. A heavier airplane requirers a higher AOA to sustain level flight. So let's say that your wing reaches Max AOA at 15 degrees, and lets say Va puts the wings at 10 degrees AOA giving you a 5 degree cushion. Then a lighter airplane needs to go slower to get an AOA of 10 degrees and a heavier airplane can go faster while maintaining that same AOA.
Now it has been a few years since my AE degree and a few as well since CFIing.
jynxyjoe
Queso King
I love this stuff.
Orange Anchor
New Member
We have had numerous accidents where the info was either not understood, was not applicable or never reached the line crew. The Pinnacle RJ crash is an example in that from what I read, most crews never heard of 'core lock-up' until after the crash. The Colgan crews saw the video on tailplane icing but again, from what I read, the Q400 and Saab are not subject to the problem. Air Florida was taught to not 'overboost' the engines and never advanced the throttles.
It's not only what you don't know but also what you know but is incorrect that can get you killed.
Am a big advocate of Reason's Swiss Cheese model.
tonyw
Well-Known Member
I like cheese. But I prefer provolone to Swiss.
Orange Anchor
New Member
Reason's model works very well but it ignores the fact that we are extremely creative in going outside the assumptions. In the Airbus crash a while back where the Capt was pushing on the yoke trying to force the airplane down to capture the ILS, he was controlling the elevator while the autopilot was retrimming the stabilzer. When it let go, the Capt was the loser ('looser' in net speak).
The Airbus officials said, "We never considered a pilot would fight with the autopilot." New disconnects were implemented.
Likewise, from what I read, Grumman said the F-14 was virtually impossible to spin and soon after its introduction to the fleet, a nugget showed 'em how to do it.
Reason's model does have some places it could improve and flex, but I do like it better than accident chain for many types of accidents; though accident chain does work for some also; though to me it implies more of a single-point/single-event failure, which is not always the case. Each has its good place though IMO.
Orange Anchor
New Member
I like Dekker's and Dismukes' look at events. It is not enough to point out what happened but ask WHY it happened. People do not crash on purpose. and while the cheese model and the chain theory make things into a neat package, as Dekker says, "Classification is not explanation." It does help create more 'barriers' but we have to remember each accident is an exception to the rule and a unique event. That takes us to FOQA and ASAPs. And that takes us to culture.
While the guy/gal in the seat has changed over the last decade and the technology has also changed, name the last time you were in a CRM or Error Management class that was attended by some high ranking official in the company.
CBpilot
Well-Known Member
:yup: For some reason that quote made me spit beer on my screen. Thank you for that on a Sunday night.
Divine Wind
New Member
You just demonstrated examples of engineering failures, imagination failures, management failures and training failures. All additional discs on the model.
Orange Anchor
New Member
As said before, we simply can not write enough rules to cover all possibilities.
When I was in the tng dept one of our guys was involved with the introduction of the F-15. The first manual was quite thin and of course, the USAF has always differed from the Navy in that in the Navy the maxim was 'if we don't say you can't, you can'. The USAF said, "if we don't say you can, you can't." And as incidents and accidents occurred, the USAF manuals got thicker and thicker.
And, one of Weiner's Laws is that with each new technology, a new potential for error is introduced. For example, prior to retractable landing gear, gear up landings did not happen.
Divine Wind
New Member
True. However, the model isn't designed for rules generation. It's an analytical tool for understanding causal factors in an accident. Once a causal factor is identified and understood, it can be mitigated.
As a retired Naval Aviator I am aware of the USAF/Army vs. Navy/USMC philosophical differences. Although Naval Aviation philosophy leans toward "if it doesn't say you can't, then you can", an aviator who exercises bad judgment (aka Headwork) will see his wings clipped....given he survives the incident.
Headwork/judgment would be another wheel on the Reason model with Aviation Decision Making (ADM). A pilot's ability to exercise good ADM can be screened for and enhanced through education. As this link states:
You are right that we can't write rules for everything, but in many instances it isn't necessary. It is like the ancient Lao Tzu quote, "Give a man a fish and you feed him for a day. Teach him how to fish and you feed him for a lifetime." A well-trained and proficient pilot has a greater chance of responding properly to a situation, regardless what it is, than a pilot only given the bare minimums to meet the standards. The Colgan accident is proving to be a textbook example of this philosophy.
Further reading: FAA AC 60-22 Aeronautical Decision Making
Orange Anchor
New Member
Decision Making and Intiution
Agreed. But there is seldom a single factor.
(never met the man but have heard lots of stories about him)
Did you see the piece in the NYTimes a few weeks ago about intuition and combat ops? Very interesting. But we aviators like to think we arrive at our actions via very controlled and pristine logic. Not so.
And while the FAA uses the term ADM, it really is just DM. And like James March says in his primer on decision making, we have to focus our minds, learn how to use the information and how to arrive at a decision. More often than not, without training, our decision making is more of a meander than a direct path.
Agreed. But there is seldom a single factor.
And that is probably a result of the culture change wherein rogues are finding it harder to survive. Think the aviator in this photo could fly in today's Navy?
(never met the man but have heard lots of stories about him)
Ah.. Ms. Orasanu. Have you met her? She, for a period of time was working with a GaTech researcher, Ute Fischer. Nice people.
Did you see the piece in the NYTimes a few weeks ago about intuition and combat ops? Very interesting. But we aviators like to think we arrive at our actions via very controlled and pristine logic. Not so.
And while the FAA uses the term ADM, it really is just DM. And like James March says in his primer on decision making, we have to focus our minds, learn how to use the information and how to arrive at a decision. More often than not, without training, our decision making is more of a meander than a direct path.
TUCKnTRUCK
That guy
In our Q manual, it pretty much explicitly states that at speeds below Va, large alternating control inputs will cause structural failure/dammage. I take that to mean, that the airplane will most likely survive a sudden excursion, but, VA isn't a ticket to just do as you like.
Firebird2XC
Well-Known Member
Great statements, all.
I was pondering this concept the other day. I remembered how in my initial private pilot training how V(a) was explained to me, and how it was usually stated "no abrupt control movements".
Later on, when I was delving more deeply into the aerodynamics and math behind such things, V(a) was explained as a defining line between the point where structural damage might occur vs. a stall.
As a young private pilot I didn't do a lot of "abrupt control movements" so I saw V(a) as an almost intellectual concept, and didn't really understand the gravity of it. Now when you consider the more realistic aspects of it, I give it a little more respect.
I was pondering this concept the other day. I remembered how in my initial private pilot training how V(a) was explained to me, and how it was usually stated "no abrupt control movements".
Later on, when I was delving more deeply into the aerodynamics and math behind such things, V(a) was explained as a defining line between the point where structural damage might occur vs. a stall.
As a young private pilot I didn't do a lot of "abrupt control movements" so I saw V(a) as an almost intellectual concept, and didn't really understand the gravity of it. Now when you consider the more realistic aspects of it, I give it a little more respect.
Cav
Former Maddog Whisperer
I think this is the key. I was told during an RPC oral that Va provides airframe protection provided only one full deflection of a control surface is made. The instructor was specifically referencing AA587.