Space Shuttle Critical 1
 

As a much younger man, I remember reading about the Space Shuttle, I was shocked to discover it had 800 parts which were classed as 'Critical 1'.

If just one of these failed it meant an almost certain catastrophic loss. Sounded way too dangerous to me.

And that got me wondering, how many Critical 1 type incidents could affect a helicopter.

Lets see:

- Blade falls off
- Cyclic fail/jam
- Collective fail/jam (jam up - you have your very own oribiter)
- Main mast fail
- Sprag clutch seize/fail
- Main gearbox seize/fail
- Tail boom off
- Tail rotor gearbox jam/off
- Frame comes apart
- Cabin comes apart/falls off
- Pilot Immobilized


What about critical 2 - life threatening but recoverable with proper action

- Throttle fail
- Fuel out
- Engine fail
- Tail rotor fail/fall off
- Fuel leak
- Electrical fail
- Minor fire
- Clutch fault
- Drive belt fault

The there's the old pilot error stuff

- Flying inside the H/V curve
- Tubulance
- Wrong control input
- Vortex ring
- Rollover
- Weather
- Not being able to land clear
- Bird strike
- Collision with ground/cables/aircraft
- Misjudgement-eg emergency practice accidents

I guess there's more I've missed.

And some you disagree with.

But what I find real interesting is the stuff that I'm normally most concerned about - eg engine failure, other mechnical fault, I class as critical 2 - recoverable in most cases.

Critical 1 I hardly even consider! Mostly these are preventable with good pre-flight checks- but when did you last really, really check the control linkages ?

And I suppose the pilot error stuff is mostly about having the right attitude/taking care.

Conclusion ?

Spend as much time and energy making sure the Critical 1 stuff doesn't happen as I spend practicing for if/when a critical 2 does.


Now where did I put that space-suit.

sw

Stop it, you're frightening the kids!
:ooh:

those could be "critical 2" if you are in the right helicopter and very lucky. ;)


About the tailboom off...
Who has the "long" version of this video?
http://www.mh-53pavelow.com/media/vi...53tailloss.avi




Aser.

Where is Lu when you need him? :(

I miss his posts.

What happened to the crew?

I will not be able to rest till I know, that break seemed to occur where the body is about as thick as a single decker coach is high,

What chance R22

Vfr

woah :ooh: , did it break where they pivot (well the naval ones, dont they pivot to save room? )

Huh? All the preflight checklists I know include checking the control linkages.

Are there some helicopters that don't?

cl12pv2s

Stepping into a Rotary is Critical 1 to me.

Where's my plank?

swsw,

Your count is way off. The typical helicopter has between 100 and 500 parts that are flight critical ("critical 1" to use your grading system.)

I think you forgot that the tail rotor itself has about 40, and its gearbox has about 20. Tail drive shafts? Main transmission interior parts? Work your way across the machine (don't forget the 100 flight control parts, each rod has two bearings, two nut-bolt sets, for example).

"The typical helicopter has between 100 and 500 parts that are flight critical..."

I imagine that figure about doubles for power assisted machines. Hydraulic pumps, sensors, rams - not to mention all the lines and valve blocks.

Ok technically the machine is still flyable if hydraulics go, unless it has additional stability augmentation...

Mart

Graviman,
No it really doesn't double, since we use redundancy to control the failure rate to very low numbers. The definition of a flight critical component is that if the component fails, the aircraft has a high probability of a mishap. With a dual hydraulic system, the probabilities of a dual failure are very low, so they are not necessarily flight critical.

Usually, as the helo gets more complex, the number of critical parts drops, as a result.

In the particular sphere that I inhabit, we use three classifications:-

(1) Primary - if it fails, you're in serious trouble

(2) Secondary - if it fails, safety of the flight is endangered but should be recoverable.

(3) Tertiary - if it fails, it's annoying.



So taking a typical helicopter:-

Primary - rotor blades, Jesus bolt, hub mechanism, engine attachments, tailrotor linkages, gearbox, main airframe....

Secondary - main flight instruments, doors, windows, duplicated hydraulic components....

Tertiary - trim, placards, backup instruments, seat cushions, furry dice...


G

(You can have fun sometimes arguing over the boundaries when classifying things for safety analysis purposes - but in general, if in doubt class upwards).

(Good grief, this is my 4,000th post. I need to get out and do more flying!)

relegation
 

Yeah Gengs, you're now downgraded and demoted to the top 10th poster of all time ! You wanna sort it out mate - you're falling behind ! Even our very own SASless is catching up at position 31 !

http://www.pprune.org/forums/memberl...ers&perpage=10

"No it really doesn't double, since we use redundancy to control the failure rate to very low numbers."

Good point well made. Been looking at single channel hydraulics too long. Power electric will improve matters further (although personal thoughts are still mechanical for light helis).

Does Sikorsky use the same hydraulic fluid as (say) Gulfstream? From memory it is phosphorus ether, and chemically attacks practically anything. Nasty stuff to have leaking...

Mart