" How I Almost Destroyed a £50 million War Plane...'

[LlamaFarmer]

A friend emailed me this link thinking I'd be interested. Thought I'd post it here for others to read also.


About "Normalisation of Deviance", or departure from SOPs, self-inflicted culture change and deterioration of safety nets.




How I Almost Destroyed a £50 million War Plane and The Normalisation of Deviance. - Fast Jet Performance (http://www.fastjetperformance.com/podcasts/how-i-almost-destroyed-a-50-million-war-plane-when-display-flying-goes-wrong-and-the-normalisation-of-deviance)

[Basil]

Another one is: 'I've always done that but do I really have to; would it make any difference if I didn't?'
That's when you find out that all the little safety bits you've built up over the years work and you start dropping them at your peril.

[glad rag]

Very good article.

Applies to us blunties too and is part of the mandatory HF training we carry out.

It can be interesting being fairly "new" to an organisation and taking a little step back and observing just what is going on....

[captplaystation]

Excellent article that many of us can relate to I am sure.

Although this "I know better" culture is gradually being filtered out of airlines, it still exists, and in less "regulated" environments, I am sure it is still rife.

[Tourist]

Although this "I know better" culture is gradually being filtered out of airlines, it still exists, and in less "regulated" environments, I am sure it is still rife.

You have to be a bit careful with statements like that, because though completely true, that is not necessarily a good thing.

"I know better" is also known as "airmanship and captaincy"

ie If all there was to being a good captain is knowing and following the rules religiously then an autistic pilot with an eidetic memory would be brilliant.

Captaincy and airmanship are all about knowing when the SOP is wrong for the situation.

That requires an "I know better" attitude.

So yes, airlines are losing the "I know better" attitude.

[chillindan]

Great article, as well as some of the others on the site!

[cappt]

In the late eighties I was a young Harrier mech and flying a jet with this sort of mechanical discrepancy was unheard of in our organization. The jet would have been grounded, it may have been authorized for a one-time flight with the gear pinned down. If need be the squadron would fly the part out from home base or a different jet.
Interesting story though, the on deployment get'er done mentality can bread all sorts of "normal deviancy"if left unchecked.

[Stone69]

Indeed an interesting story. It's been a long time since I flew single seat jet, but I can't help but think I might have gone inverted and tried the negative G heading away from the hard stuff rather than pointing at it....

[Tourist]

Indeed an interesting story. It's been a long time since I flew single seat jet, but I can't help but think I might have gone inverted and tried the negative G heading away from the hard stuff rather than pointing at it....

I think it was zero G.

Difficult to get that without a ballistic trajectory....

[captplaystation]

Tourist,

point taken, but, as per the original story, I was thinking of making it up as you go along, rather than utilising imagination/experience to get you out of a dire situation.

I am no fan of the "SOP MONKEY" mentality that seems to have become the modus operandi in one particular large loco, where visual approaches are frowned upon, well, unless accompanied by some convoluted "double brief". I am thinking more in terms of the days when FO's had to remember 20 different sets of SOP's to suit the 20 Capts they flew with, some of which were thinking perhaps a little too far out of the box for everyones well being.

[Chronus]

Here is another from the confessional :

Speed Is Life - Plane & Pilot Magazine | PlaneAndPilotMag.com (http://www.planeandpilotmag.com/speed-is-life.html)

Deviance normalised by fast recall of basics of staying aloft, never mind the G`s, the gear or anything else. Thrust is a must.

[JohnFTEng]

I agree with Stone69 - inversion was a much better option.
Thread drift warning!
As a very junior Flight Test Engineer some 40 years ago I needed a -1g/M1.0/1,000ft test point The senior FTE looked a my proposed push to -1g and said "not sure the pilot will like that too much, lets just roll inverted and get a gentle push up" Test point achieved every one happy

[LlamaFarmer]

I agree with Stone69 - inversion was a much better option.
Thread drift warning!
As a very junior Flight Test Engineer some 40 years ago I needed a -1g/M1.0/1,000ft test point The senior FTE looked a my proposed push to -1g and said "not sure the pilot will like that too much, lets just roll inverted and get a gentle push up" Test point achieved every one happy


I haven't flown fast jets and not done that much aerobatics, but could they not have climbed up into the 10s of thousands, above the cloud (or even in the cloud with radar separation) before attempting a level outside turn pushing constant -ve G around the turn until it's up and locked?


Not that they should have done that either, but it strikes me as a safer option than diving at the ground

[Tourist]

Some misunderstandings here.

1. There is no need to "gently push up" once inverted to get -1G. You are already there just by being inverted.

2. As stated, the nature of the problem required zero G, not negative G. -1G would be just as bad under those circumstances as +1G.
0G can only be achieved in a ballistic path (or at a legrange point, but that would be very tricky to achieve under these circumstances!)

3. "I haven't flown fast jets and not done that much aerobatics, but could they not have climbed up into the 10s of thousands, above the cloud (or even in the cloud with radar separation) before attempting a level outside turn pushing constant -ve G around the turn until it's up and locked?"

Their idea was misguided.
Yours is insane, and shows a little lack of understanding of G.
Why turn? What is the added benefit?

[LlamaFarmer]

To get the -ve acceleration, but having re-read it I misunderstood as I thought I'd seen below 0g but actually was under (at) 0g.

My bad for skim reading.

[RAT 5]

If you were inverted, level, and activated gear up, would the gear not fall into the gear bay & lock under gravity?

[No Fly Zone]

"Important' event or not, I would not have flown that airplane on other than a low, slow ferry and with pinned gear, en-route to a Mx base. No!

[Tourist]

"Important' event or not, I would not have flown that airplane on other than a low, slow ferry and with pinned gear, en-route to a Mx base. No!

Thank you for letting us know.
We will all rest easier knowing of your wisdom.

[Sheep Worrier]

I fear (or she) had completely missed the point of the (rather excellent, IMHO) article.

[Fortissimo]

Tourist, there are indeed some misunderstandings on here. You do not get -1g simply by rolling inverted. You have to remain in level flight to achieve that. But I don't have a monopoly on wisdom, so please feel free to give me the benefit of yours so I can rest easy as well.

[Tourist]

Tourist, there are indeed some misunderstandings on here. You do not get -1g simply by rolling inverted. You have to remain in level flight to achieve that. But I don't have a monopoly on wisdom, so please feel free to give me the benefit of yours so I can rest easy as well.

Yes you do.
Simply rolling inverted gives you exactly -1g.

Doing anything else does not, i.e. not remaining in level flight.


I can make this easier for you if you want, but I thought the phrase "simply" was clear enough.

Here goes.

Roll inverted.
Don't do anything else.
Don't apply full left or right pedal.
Don't change the power setting.
Don't deploy speedbrakes.
Don't deploy flaps.

Just roll inverted and continue to maintain non accelerative flight with reference to the mean surface of the planet you are currently orbiting.

At this point the only acceleration you are experiencing is the acceleration due to the local gravity of the position you are in. This is generally considered to be a constant of approx. 9.81m/s2 on the surface of planet earth with obvious local variations for velocity of aircraft, position and height on planet earth and as affected by our orbit around the sun and the moons orbit around us.
We call this 1g, or in the event we are discussing, -1g due to the orientation of the aircraft




Personally I think my first statement covered the relevant facts and was more succinct.
If you want any more clarification, please get back to me.:ok:

[Basil]

If you roll inverted and wish to maintain level flight you will require to apply more thrust - unless you have a symmetrical aerofoil with a zero angle of incidence.

[Tourist]

If you roll inverted and wish to maintain level flight you will require to apply more thrust - unless you have a symmetrical aerofoil with a zero angle of incidence.

Not necessarily, but good general point.

I should have said apply the correct amount of thrust to maintain speed.

[deefer dog]

Not necessarily, but good general point.

Why was Basil's statement not necessarily correct Tourist? Please explain.

[Tourist]

Why was Basil's statement not necessarily correct Tourist? Please explain.

Because depending on the aerofoil and angle of incidence, it is possible that you would have to reduce thrust.

Come on, keep up.;)

[edmundronald]

As Tourist points out, any non-accelerative (constant-speed vector ) trajectory will give you constant pilot-relative 1g. You can then choose to apply this 1g in any pilot-relative direction you want by rotating the plane into any acceptable attitude.

Presumably vectored thrust fly by wire aircraft can maintain very strange constant-speed-vector attitudes, in the same way as powered aircraft can maintain constant-speed-vector attitudes quite different from gliders.


Edmund

[deefer dog]

Because depending on the aerofoil and angle of incidence, it is possible that you would have to reduce thrust.

Err...but as basil pointed out, in the case of a symmetrical airfoil, with zero angle of incidence, that is not the case. So I ask again, why "not necessarily" in response to basil's post?

[Tourist]

Err...but as basil pointed out, in the case of a symmetrical airfoil, with zero angle of incidence, that is not the case. So I ask again, why "not necessarily" in response to basil's post?

Ok, I'll try again.

It is possible, would you agree, to have an asymmetric aerofoil that has superior efficiency inverted than the right way up. It is also possible to mount a wing with an angle of incidence giving reduced drag inverted.

Under both or either of those circumstances, it is possible to have a reduced thrust requirement inverted than the right way up.

Not likely, but possible, and in the realms of this "aeronautic basic concepts shlong measuring" debate which we are all involved in, possible is plenty.

Hence "not necessarily, but good general point"

As I said, come on, keep up!;)

[effects]

There are 2 reasons I find this 'story' a load of bs,
A- no engineer would suggest this solution unless it was a one off rtb.
B- surely select the gear count to ten before going negative g would be a far smarter solution or as suggested inverted flight before gear retraction.

[Tourist]

Point A is a fair point.
Point B is another misreading. It was zero not negative they wanted.

[JammedStab]

How about just doing the whole maneuver in IMC(if you decide to do the maneuver that is).

[papazulu]

Simply rolling inverted gives you exactly -1g.


No you are not.

The aerofoil (or for what matters the entire airframe) doesn't know what's up and what's down as long as the entire contraption is flown straight and lever at constant speed (for relatively short distances the said planet can be considered flat). Drag might be different but that's already another story.

+ or - are mathematical conventions, depending upon the referencing system one's choose. Since weight is a "standard" force experienced by everything on earth, it has been chosen to be positive, perpendicular to the surface and directed to the centre. Wanna go zero-g or negative? Get high the push down sharply...

PZ :rolleyes:

[CONSO]

The aerofoil (or for what matters the entire airframe) doesn't know what's up and what's down as long as the entire contraption is flown straight and lever at constant speed

True- but what is missing from this ' erudite' discussion is the concept of up versus down.

For a standard airfoil - it is shaped such that the ( lift vector ) in normal flight is UP which allows the plane to fly level and generally at right angles to the gravity vector ( DOWN ) in normal flight. When the two vectors ( lift versus gravity or UP versus DOWN ) balance- the plane flys level at some elevation above local earth.

BUT if you turn the same wing inverted or upside down , then the LIFT VECTOR ADDS TO THE GRAVITY VECTOR, and absent some other forces the plane will go down, still in level flight -at least for a while.:ugh:

Keep in mind that I am talking steady state conditions- absent any other control manipulations or forward vector changes in speed- momentum which can delay the result net DOWN for a while.

[megan]

You do not get -1g simply by rolling inverted. You have to remain in level flight to achieve thatYou don't have to remain in level flight. Rolling inverted and maintaining the pre roll power setting and airspeed will see the aircraft accelerate into and establish a fixed rate of descent due to increased drag (symmetrical airfoils aside). Once the steady state inverted descent is established -1 "g" will be experienced. Accelerating to the steady state descent will see >-1 "g", -.8 as an arbitrary example.

[Tourist]

BUT if you turn the same wing inverted or upside down , then the LIFT VECTOR ADDS TO THE GRAVITY VECTOR, and absent some other forces the plane will go down, still in level flight -at least for a while.:ugh:


That's exactly right, and that is why when doing a quick aileron roll, you find the aircraft accelerating downwards at nearly 20 m/s2 during the inverted phase.....

....oh, wait.

[Tourist]

You don't have to remain in level flight. Rolling inverted and maintaining the pre roll power setting and airspeed will see the aircraft accelerate into and establish a fixed rate of descent due to increased drag (symmetrical airfoils aside). Once the steady state inverted descent is established -1 "g" will be experienced. Accelerating to the steady state descent will see >-1 "g", -.8 as an arbitrary example.

Not really true if we are using the aircraft as the basis of what is up or down re g.

As the angle of descent increases, the g relative to the plane of the aircraft's usual up or down drops to zero as the aircraft reaches the vertical.

ie gravity will be pulling directly towards the nose once vertical so zero g relative to gear going up or down.

Sorry, that is badly explained, but I hope you understand what I mean.

I am told that test pilots sometimes do test in an angle of descent for specifically this reason to get less than one g with respect to the aerodynamic surfaces etc despite being in a steady state.

Despite the drop in negative g experienced by the undercarriage due to a descent, you could bring that negative g back up to -1g by throwing in a turn.

[joe two]

interesting ,

I always thought I'd have -1G as I am pushing the stick to stay at level while inverted.
Pushing the stick further gives -2G or more (but then I am not flying level anymore) up to e.g. an inverted loop with -3G up to -4G.

That's the way I explained the -1G inverted in the simplest terms , still correct I hope :8 ?

[Tourist]

I always thought I'd have -1G as I am pushing the stick to stay at level while inverted.


The fact that if you build a symmetric aerofoil aircraft with zero angle of incidence it is possible to have zero trim change inverted suggests that the push is not what is giving you the negative g....

[joe two]

yep , convinced ...

[BBK]

Am I the only one who is bemused that the folks posting here seem to have missed the point of the article? I'd call it a classic I Learnt About Flying From That (ILAFFT) piece. Normalization of deviation, Human Factors etc. just saying...

BBK

[Pozidrive]

You're not alone BBK, love the irony!

[megan]

BBK, discussions often take off on a new direction, and an alert individual may learn something new.

Tourist, being as thick as I am I could make no sense of your post #36. To check we are on the same page a couple of questions. OK, three. :)

Say we have a skydiver hanging onto the edge of a balloon basket. What "g" is he experiencing under the following circumstances

1. While hanging onto the balloon basket
2. The exact instant he lets go of the balloon basket
3. When he reaches terminal velocity

[CONSO]

Say we have a skydiver hanging onto the edge of a balloon basket. What "g" is he experiencing under the following circumstances
1. While hanging onto the balloon basket
2. The exact instant he lets go of the balloon basket
3. When he reaches terminal velocity 1 = 1 g
2 = 1 g
3 = 1 g

assumes balloon is stationary and NOT accelerating up or down AND he does not use a fly suit or wing suit but drops like the proverbial brick

[pchapman]

Re: the -1g push that's a side show to the thread:

Wouldn't a push typically be needed when you roll inverted? (Even if the aircraft is a more symmetrical type, and not draggier and less aerodynamic upside down.)

My off-the-cuff aerodynamics isn't the greatest so I won't go into a ton of detail. But I can refer to a what a couple well regarded aerobatic pilots wrote.

Neil Williams in his book Aerobatics in the '70s:

"The more stable the machine in normal flight, the heavier it will be in inverted flight on the controls; for example, if the tail-plane is set at a high negative incidence on the fuselage, it will give strong longitudinal dihedral, and therefore a powerful restoring force in the event of a disturbance. This, coupled with a forward C.G. can make it very tiring to hold the push force required for inverted flight, and it may be impossible to trim it out. On aeroplanes of this sort, one has to use the trimmer to fly aerobatics, and this will not result in a good performance. Since most aerobatic machines have some positive longitudinal stability , there will always be a push force in inverted flight. By trimming nose heavy, we can compensate to some extent for this."

Eric Mueller in Flight Unlimited similarly writes about trimming for 0g. If one trims for 1g, then one will have to push for level -1g. If one trims for 0g there will be a little pull at 1g (at a given speed) and still some push for -1g. So a push is expected.

============

As for "Normalization of Deviance":

While I like the concept, I think it may be overused, as it is a handy and erudite sounding catch phrase. It seems pejorative about any change, as if there is only one possible correct way. Sometimes that is in a sense true, because if the boss or the manual says there is one way, then that is supposed to be the right way. Or everyone might indeed agree that one way is far more right than another.

If procedures aren't that clear cut though, then it is a kind of 'blame the underling' strategy. If the boss' way results in an accident, well, it's just an unfortunate accident and maybe things will have to change in the future. But if the underling's way results in the accident, then the underling pilot may have been guilty of normalization of deviance.

So one has to be careful about defining what is normal or acceptable. There may be no absolutes involved.

The "How I almost destroyed..." article does talk about Normalization of Deviance as both something that can happen to individuals (like him & his back seater doing the 0g gear up procedure) and something affecting an organization (e.g, Red Arrows procedures getting out of step with other parts of the RAF).

One has to be careful not to conflate the two. If it is something happening in an organization, where it has been accepted as a norm to do things in a way unlike in the dusty manual on the shelf -- and the boss hasn't stepped in -- then it may not be an individual pilot's fault. He isn't normalizing any deviance -- he's just following the de facto standards of the squadron. As far as he knows, his procedures are normal and not deviant.

Just my opinion as an amateur observer of aviation human factors.

[Tourist]

1 = 1 g
2 = 1 g
3 = 1 g

assumes balloon is stationary and NOT accelerating up or down AND he does not use a fly suit or wing suit but drops like the proverbial brick

No.

2 is zero if we use the only sensible reference frame.

You can check this by fitting a g meter to the man. It will read +1/0/+1

We can go into a little more depth if you want, but if you disagree, be aware that you are arguing with Einstein, not me.

The elevator, the rocket, and gravity: the equivalence principle ? Einstein Online (http://www.einstein-online.info/spotlights/equivalence_principle)

[Loose rivets]

Beat me to it on Equivalence. The fascinating thing is that the instant his fingers stop resisting gravity, he is weightless (no real airflow yet.) No transitional time.

I'm perplexed by the thread drift since it sometimes seemed to veer, erm, bunt off into talking of negative g rather than attaining 0 g. Thread drift is usually beneficial, nit-picking, quite different.

I'm sure the pilot was able to fly level inverted without much thought and then the issue becomes - what would be shown on a g-meter?

Neil Williams. For those not around back then, the man knows a little about inverted flight. Having suffered what might be called, asymmetric dihedral, i.e. a broken wing, he flew back to base inverted, flipping the right way up for the landing. Nifty.

Zlin wing Structural Failure Report - Neil Williams (http://historic.aerobatics.org.uk/repeats/zlin_wing_failure.htm)

[Mozella]

1. There is no need to "gently push up" once inverted to get -1G. You are already there just by being inverted.

Surely I'm not the only in this thread who's flown inverted. There is indeed a need to "push" once inverted. I'll see if I can explain it.

A trimmed aircraft in level, unaccelerated flight is usually presented in basic aerodynamic texts books with four opposing vector arrows pointing up, down, forward, and aft representing, in order, lift, gravity, thrust, and drag. We can ignore thrust and drag for the moment. The g meter will read 1 in this instance.

If the aircraft is rolled inverted without making any other changes then the lift vector and gravity vector arrows are both pointing in the same direction. The aircraft will accelerate toward the earth rather rapidly unless the pilot does something to prevent it.

If level inverted flight is the goal, then the pilot will push forward on the stick far enough to produce a lift vector equal the the weight of the aircraft or, put another way, he will produce sufficient negative lift to offset the force of gravity. A new drawing will show the same four vector arrows, but this time the lift vector will be extending from the belly of the aircraft; i.e. the vertical forces on the aircraft are reversed. To maintain level inverted flight in a conventional aircraft, you gotta' push to overcome the significant out of trim condition.

[Tourist]

Mozella

It is possible/probable you may have to re trim when inverted, but that is different from "lets just roll inverted and get a gentle push up"

I would describe the action required to fly level inverted as applying forward pressure to maintain straight and level until re-trimmed. Once re-trimmed, no push will be required.

I believe I am correct in thinking that when the phrase "lets just roll inverted and get a gentle push up" was used he meant to push the nose of the aircraft up from the horizontal to get negative g.

[megan]

Tourist & Loose rivets, no fooling you two. The instant he lets go he is experiencing zero g. This fact was used to good effect in the production of lead shot and musket balls in days of old, since a liquid in zero g will form a perfect sphere.

NASA has what is called a "drop tube" at Brook Park, Ohio, in which they conduct zero g experiments in a vacuum environment. The working area of the tube is 432 feet in depth and 20 feet in diameter, allowing 5.18 seconds of zero g when the experiment is dropped.

[Tourist]

Tourist & Loose rivets, no fooling you two. The instant he lets go he is experiencing zero g.

Though not all of him, obviously.....;)