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B6 Makes An Emergency Landing Due To Speed Indicato  
User currently offlinelke2fly From United States of America, joined May 2011, 70 posts, RR: 0
Posted (2 years 9 months 2 weeks 1 day 14 hours ago) and read 3432 times:
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Today I read that a B6 had to make an emergency landing in PBIA do to a speed indicator problem. I'm just curious because I don't know how this instrument effects a flight beside how fast your traveling, but how would speed indicator cause a emergency landing. Is there a back up system thats shows the speed that would allow a flight to continue? Sorry if this is a dumb question.

15 replies: All unread, jump to last
 
User currently offlineBMI727 From United States of America, joined Feb 2009, 15489 posts, RR: 26
Reply 1, posted (2 years 9 months 2 weeks 1 day 12 hours ago) and read 3395 times:

Quoting lke2fly (Thread starter):
I'm just curious because I don't know how this instrument effects a flight beside how fast your traveling,

If you don't know how fast you are going, you can get yourself in really deep shit really quickly and not even know it. It is nearly impossible for pilots to fly without accurate speed data from the instruments and completely impossible for the autopilot to fly with bad data.

More than one aircraft has been lost due to problems in the pitot-static system.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 2, posted (2 years 9 months 2 weeks 1 day 10 hours ago) and read 3363 times:

First of all, what they said was due to a speed indicator problem. Or even more likely they explained it in more detail and the reporter dumbed it down. So what actually happened is very probably more complex than what was reported.

Certainly speed indication is multiply redundant, but as BMI727 says indicated airspeed is a crucial bit of information. You do not want to be without it.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinebristolflyer From United Kingdom, joined May 2004, 2271 posts, RR: 0
Reply 3, posted (2 years 9 months 2 weeks 1 day 5 hours ago) and read 3264 times:

Don't aircraft have GPS based speed monitoring? I know that this would give groundspeed not airspeed, but it could be pretty useful if the pitot tubes aren't working. I thought this about the AF Airbus that went down in the Atlantic.


Fortune favours the brave
User currently offlineBMI727 From United States of America, joined Feb 2009, 15489 posts, RR: 26
Reply 4, posted (2 years 9 months 2 weeks 1 day 5 hours ago) and read 3242 times:

Quoting bristolflyer (Reply 3):
I know that this would give groundspeed not airspeed, but it could be pretty useful if the pitot tubes aren't working.

Only to a point, plus wind information necessary to derive any useful information would come from the air data computer, which I think in most cases uses many of the same sensors as the airspeed indicator.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlinelke2fly From United States of America, joined May 2011, 70 posts, RR: 0
Reply 5, posted (2 years 9 months 2 weeks 15 hours ago) and read 2986 times:
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Thank you to all you for responding ,I understand how important that piece of equipment is and why the B6 had to land. I just thought there was back up instruments that would not cause it to make an emergency landing. Im sure they down played it like Starlionblue stated.

User currently offlineMaverick623 From United States of America, joined Nov 2006, 5429 posts, RR: 6
Reply 6, posted (2 years 9 months 2 weeks 13 hours ago) and read 2960 times:

Quoting bristolflyer (Reply 3):
but it could be pretty useful if the pitot tubes aren't working.

Eh... not really, at least in an airliner at altitude. You would have to have fairly specific wind information to even come close to guessing your airspeed. Even then, while getting behind the airplane in a 172 might not be too big of an issue, getting behind in an Airbus going at least 200MPH is not good at all.

Quoting lke2fly (Reply 5):
I just thought there was back up instruments that would not cause it to make an emergency landing.

The backups are there to ensure that an emergency landing can be made when something does go wrong. A pilot will never continue the flight if there is only one system left with no other backups.

Quoting lke2fly (Thread starter):
Sorry if this is a dumb question.

It's a rookie question... but rookies advance by asking them. Don't sweat it.

Quoting Starlionblue (Reply 2):
So what actually happened is very probably more complex than what was reported.

In my experience, common problems are airspeed splits (where two or more indicators show different speeds), or a complete airspeed failure on either side of the cockpit.



"PHX is Phoenix, PDX is the other city" -777Way
User currently offline330guy From Ireland, joined Nov 2010, 453 posts, RR: 2
Reply 7, posted (2 years 9 months 2 weeks 7 hours ago) and read 2881 times:

This reminds me of a story my Dad told me about a UPS 742 many years ago in DUB, It had just undergone maintenance and was going out for a test flight. After they took off the PIC noticed they were getting no speed indication so declared an emergency, The were vectored over Dublin Bay and told to wait for assistance, They were told that an Air Corp jet was on its way to fly alongside and radio the current speed and escort them back to DUB.
While they were waiting the PIC saw a break in the clouds and had a clear sight of 28 (it may have been 27 at the time but how and ever) And advised he didn’t want to wait around so was making an approach, Here’s where it gets interesting, This 747 had a system that automatically retracted the flaps from 30 to 25 I believe if the aircraft was travelling over 220kts(again this is hazy as I was told a few years ago so the figure could be slightly wrong) I don’t know if it was standard in 747’s at the time or an added extra but it was a new feature and the aircraft was also pretty new.

While on finals only a couple of miles out the flaps retracted automatically from 30 to 25 and the aircraft burst every tyre on landing and done some damage to the MLG, Its not known the speed at landing but its believed to be close to the 230kt mark. Turns out the pitot covers were left on after maintenance had finished with the aircraft, it’s not known by the maintenance crew how they managed to take off with no speeds indicated (V speed calls) or why they didn’t notice but I’m sure the crew got a bit of a bollicking when they got back to Memphis



Aircraft flown: a300/10/20/21/30/40, b727/37/47/57/67/, DC9, MD80-90, l1011, f50, atr42/72, shorts360, pc12
User currently offlineboeingfixer From Canada, joined Jul 2005, 525 posts, RR: 0
Reply 8, posted (2 years 9 months 2 weeks 6 hours ago) and read 2854 times:

Quoting BMI727 (Reply 4):
Only to a point, plus wind information necessary to derive any useful information would come from the air data computer, which I think in most cases uses many of the same sensors as the airspeed indicator.

They are one and the same. The Digital Air Data Computer(DADC) IS your airspeed in as much as the information displayed to the pilots is from the DADC's.

Wind information is derived from the Inertial Reference system.

Cheers,

John



Cheers, John YYC
User currently offlinejetlagged From United Kingdom, joined Jan 2005, 2532 posts, RR: 24
Reply 9, posted (2 years 9 months 1 week 3 days 22 hours ago) and read 2448 times:

Quoting bristolflyer (Reply 3):
Don't aircraft have GPS based speed monitoring? I know that this would give groundspeed not airspeed, but it could be pretty useful if the pitot tubes aren't working. I thought this about the AF Airbus that went down in the Atlantic.

Not much use at altitude because GPS would give you true airspeed (in zero wind). The crew need to fly according to Indicated Airspeed (IAS). Rather than using GPS, pitch attitude (in level flight) gives a rough indication of angle of attack and so airspeed if IAS indication is lost.

Quoting 330guy (Reply 7):
This 747 had a system that automatically retracted the flaps from 30 to 25 I believe if the aircraft was travelling over 220kts(again this is hazy as I was told a few years ago so the figure could be slightly wrong) I don’t know if it was standard in 747’s at the time or an added extra but it was a new feature and the aircraft was also pretty new.

It's called Flap Load Relief and all 747's have it in some form or other.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineBMI727 From United States of America, joined Feb 2009, 15489 posts, RR: 26
Reply 10, posted (2 years 9 months 1 week 3 days 22 hours ago) and read 2439 times:

Quoting boeingfixer (Reply 8):
Wind information is derived from the Inertial Reference system.

Maybe I am missing something, but doesn't that still leave the plane with the same problem? The IRS will measure and calculate all of the plane's acceleration, velocity, and position change, but without data from the pitot-static system it can't tell what of that came from airspeed and what came from wind, can it?

The IRS can say that I flew 500 NM in 1 hour, but without reliable airspeed data it can't tell me if I went 600 knots with a 100 knot headwind or 400 knots with a 100 knot tailwind, right?



Why do Aerospace Engineering students have to turn things in on time?
User currently offline330guy From Ireland, joined Nov 2010, 453 posts, RR: 2
Reply 11, posted (2 years 9 months 1 week 3 days 22 hours ago) and read 2437 times:

Quoting BMI727 (Reply 10):
The IRS can say that I flew 500 NM in 1 hour, but without reliable airspeed data it can't tell me if I went 600 knots with a 100 knot headwind or 400 knots with a 100 knot tailwind, right?

This is correct I beleive

Quoting jetlagged (Reply 9):
It's called Flap Load Relief and all 747's have it in some form or other.

Cheers, I know the 757/767 have it but didnt know the classic 74's did as standard too



Aircraft flown: a300/10/20/21/30/40, b727/37/47/57/67/, DC9, MD80-90, l1011, f50, atr42/72, shorts360, pc12
User currently offlineB747FE From Hong Kong, joined Jun 2004, 230 posts, RR: 4
Reply 12, posted (2 years 9 months 1 week 3 days 16 hours ago) and read 2397 times:

Quoting BMI727 (Reply 10):
Quoting boeingfixer (Reply 8):
Wind information is derived from the Inertial Reference system.

Maybe I am missing something, but doesn't that still leave the plane with the same problem? The IRS will measure and calculate all of the plane's acceleration, velocity, and position change, but without data from the pitot-static system it can't tell what of that came from airspeed and what came from wind, can it?

Although normally the inertial system receive TAS & barometric altitude from the CADC, it can perform the required calculations without them and the performance is only slightly degraded.
Indicated wind component (Crosswind) only becomes inaccurate during a sideslipped approach, but that's another story.



Quoting 330guy (Reply 11):
I know the 757/767 have it but didnt know the classic 74's did as standard too

Different variants of the same system for different models (freighter, passenger or SP) but basically all 747 have flap load relief.

Regards,
B747FE.



"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
User currently offlineboeingfixer From Canada, joined Jul 2005, 525 posts, RR: 0
Reply 13, posted (2 years 9 months 1 week 3 days 16 hours ago) and read 2396 times:

Quoting BMI727 (Reply 10):
Maybe I am missing something, but doesn't that still leave the plane with the same problem? The IRS will measure and calculate all of the plane's acceleration, velocity, and position change, but without data from the pitot-static system it can't tell what of that came from airspeed and what came from wind, can it?

The IRS can say that I flew 500 NM in 1 hour, but without reliable airspeed data it can't tell me if I went 600 knots with a 100 knot headwind or 400 knots with a 100 knot tailwind, right?

Without the IRS you will never get wind speed and direction. The IRS does need an input from the CADC's for airspeed data but you said:

Quoting BMI727 (Reply 4):
wind information necessary to derive any useful information would come from the air data computer

That is entirely incorrect. The CADC's on their own do not calculate ANY wind information. They calculate IAS, TAS, Mach, altitude, vertical speed, TAT, SAT, AOA... etc.

In simple terms I was entirely correct in saying that the wind information is derived from the IRS. I didn't feel the need to state that the IRS requires air data as it didn't relate directly to your comment. So, in the end, no IRS no wind data.

Cheers,

John



Cheers, John YYC
User currently offlineBMI727 From United States of America, joined Feb 2009, 15489 posts, RR: 26
Reply 14, posted (2 years 9 months 1 week 3 days 15 hours ago) and read 2381 times:

Quoting boeingfixer (Reply 13):
So, in the end, no IRS no wind data.

Why does it need to be IRS? Couldn't GPS, which also calculates ground speed and position, perform the same function?

Calculating wind speed requires air data and ground speed information, so is there any reason why IRS is suitable for this and GPS wouldn't be, other than practical concerns like potential inability to locate satellites?



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineboeingfixer From Canada, joined Jul 2005, 525 posts, RR: 0
Reply 15, posted (2 years 9 months 1 week 3 days 15 hours ago) and read 2375 times:

Quoting BMI727 (Reply 14):
like potential inability to locate satellites?

There's the catch. Whereas the IRS is self contained, a stand alone GPS relies totally on external sources.

The IRS is a very reliable system. Where the GPS comes in is to refine the IRS position via updating although it plays second fiddle to DME updating. On the systems I'm familiar with the IRS is the main reference tool. For position updating DME is preferred as their positions don't require an ever changing almanac. The last used for position updating is the GPS.

Anyway this is all far beyond the original subject of this thread so I will let this one lay for another day.

Cheers,

John



Cheers, John YYC
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