PDA

View Full Version : Static System


HEALY
21st Oct 2004, 05:01
Just watched very good doco on the AeroPeru crash with the tape left on the static system. Very good detail and voice recorder made for interesting if not frightening listening.

Although an ATPL license holder I have tried looking for info from my study guides on static systems and still have trouble answering a few things.

1) Do larger jets have an alternate static source from withing the aircraft (like a Baron for example) which can be used if problems arise like that on the b757?

2) A mention was made in the doco that the IAS was thru the roof with high speed warning and the stick shaker operating at the same time. In a high speed stall does the stick do anything or is there only an oral/anunciator warning?

I for one minute do not want to criticise the crew at all however im curious to know what methods of flying you would adopt in this scenario. Power + Attitude to give performance?

john_tullamarine
21st Oct 2004, 06:46
Looking to your last question .. definitely thrust and body angle (as appropriate to aircraft configuration).

One of the exposure exercises I use in the later stages of sim endorsement training is a complete failure of all PS kit, radalt, etc during the takeoff rotation - if I can't fail it from the backseat then I cover up the dial. The crew ends up with absolutely nothing to give them speed, height, etc.

Exercise is to fly the aircraft back to the aid, enter the pattern, and shoot an ILS to landing - with nil assistance from the organist in the back and all in min weather conditions.

Provided that the folk have been briefed as to useful strategies and their basic I/F is OK, the exercise is not a major difficulty - although it might get a bit sweaty for the guys actually doing the work ....

BOAC
21st Oct 2004, 09:21
In a high speed stall does the stick do anything or is there only an oral/anunciator warning - Healy - I'm not familiar with the 757 but I think you are a little confused there - the 'High Speed Warning' is (normally) driven by the airspeed (hence 'confused' in this case) whilst the low speed stall warning (stickshake) is (normally) driven by airstream attack angle (probably correct in this case). That is a vane on the fuselage side and would probably have been unaffected.

I cannot imagine there being any warning of a 'high-speed stall' on a 757. Normally the clue is airframe buffet if you try to pull too much 'g' at high speed.

OOI, the BAE Lightning and Folland Gnat had large, attention grabbing main Attitude Indicators and the recommendation was if it 'froze', cover it up with a 'sticky patch' - I used to have one stuck on my bone-dome just in case. Otherwise the visual input from the topsy attitude could be overwhelming. I think if the 757 incident happened to me (and if I had time, space and brain capacity!) I'd be getting bits of paper torn up to cover the 'false' instruments - and asking for chewing gum from anyone on board to stick them on! They can produce very disorientating

Flight Detent
21st Oct 2004, 11:11
I just couldn't believe it all,

It was just like watching "Who wants to be a Millionaire" at my place, where I was literally yelling out what I thought were the 'answers'!

I realise both the normal and alternate static ports were covered, and all those indications were present, though both the MACH TRIM and RUDDER RATIO indications were not of any great concern.

Both pilots, I'm thinking, had instrument displays quite similar to the B737NG, where TAS, wind and Ground speed are displayed on the pilots PFDs.
If not, the FMCs both have ground speed and wind indication.
I'm ignoring GPS as they don't seem to have had it fitted.

Also, on descent thru 2500 feet AGL, both Rad Alts would have chimed-in and accurately displayed altitude whilst the airplane remained below 2500 feet, I know they were operating, the TERRAIN, TERRAIN warning was very evident.

So, with a reasonably accurate IAS indication, a very accurate altitude indication, contact with Lima Radar on VHF to give radar vectors to the ILS, no need to climb above 2500 feet as the vectors could avoid any high ground (Lima's on the coast).

Both the ILS receivers were not affected by the static problems, why couldn't they fly the acft to a safe landing?

I guess the same 'ol saying still applies, no FE and nobody on board who knows how the thing works, how many times!!

Cheers (I think!)

FD

HEALY
21st Oct 2004, 13:18
Thanks for the responses guys, Further to what your saying BOAC does Boeing have Pitch Limit Indicators on the PFD's so help prevent a stall attitude being reached?

The other thing which wasn't mentioned at all was how the VSI was functioning. Surely if all Pitot/Static instruments fail then something would have twigged, still, dont want to speak ill of the dead.

BOAC
21st Oct 2004, 17:58
Don't know about the PLI on 757, but as you and JT have said, Power and attitude plus Rad Alt would have saved the day ...........BUT, and a BIG BUT, this is ARMCHAIR diagnosis, and as you can see Flight Detent would have got it wrong relying on GS readout from the FMC - even now from the armchair!

I tried to put myself in their place, with all the conflicting, illogical warnings, noises, ATC inputs, stick shake etc, and I HOPE I would have managed to sort it out - but I do NOT know. It must have been a pretty horrendous cockpit to be in.

BOAC
22nd Oct 2004, 17:30
My mistake, CM and apologies to FD.:{

Ka8 Flyer
22nd Oct 2004, 18:31
Hi guys!

As this scenario has been on my mind for quite a few years, I'd like to add a few things.

I definetely don't want to say anything to the point of "boy those guys were dreadful pilots" as we now know most of the facts of what happened on that day and they only had a few minutes to analyze the situation and their "solution" didn't work out.

There were, however, mistakes made and I am pretty sure such a scenario is recoverable if it happens outside a sim environment. I watched quite a few crews experience the same scenario in the sim. Everyone did ok - of course, as they knew something was gonna fail...

Regarding the statement above that VSI info is not static dependent and only IRS dependent, is not quite accurate. Correct, the IVSI used today does _require_: IRS data, but its not the only source of info. It needs both static and IRS data to function. IRS data is used to get a quick rough estimate of VSI through the vertical acceleration. This is then adjusted by the ADC's static info. So in a situation where the static is blocked, the VSI needle would most probably just fluctuate around 0 as it recieves info from the IRS that the aircraft is accelerating vertically (provided vertical speed is not constant), but the ADC will tell the VSI that there is no difference in static pressure, hence the needle will return to 0.

The only reliable data in such a scenario would be your EADI and GS data (provided the IRU's were recently aligned). Still, you should be able to decide whether you are stalling or overspeeding. Also, AoA indications are correct (stick shaker). The QRH includes thrust and pitch info which can be used in a scenario such as this.

There is another trick to determine AGL (without having to be below 2500 ft):
use the weather radar! Set a tilt of -6.5 and check the range at which you get ground returns. Multiply this by 1000 and voila, you have your AGL. Also works in the sim!

Obviously, surviving this scenario requires thorough info of the aircraft's systems and how data is aquired and used. Unfortunately, some pilots don't know their a/c that well.

Regards,

Mark

BOAC
23rd Oct 2004, 16:06
Hear hear CM - Im just glad I watched that from my armchair and not from the cockpit.