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atlh2oskier
Topic Author
Posts: 3
Joined: Wed Apr 07, 2004 9:07 am

Airspeed Probes And Ground "tags"

Wed Jul 21, 2004 7:33 pm

Can someone explain the type of information that is collected by the metal probes on the nose of aircraft? I am assuming these are used for the collection of data related to airspeed, windspeed, altitude, etc.

Also, when on the ground, I routinely see these probes covered with orange "tags" as shown in this G-V picture:


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Photo © Tony Silva - Madeira Spotters



Are these probes sensitive to the point that they need to be covered while the plane is on the ground? Is there some other reason for this?

Thanks!
 
FinnWings
Posts: 633
Joined: Fri Oct 24, 2003 6:03 am

RE: Airspeed Probes And Ground "tags"

Wed Jul 21, 2004 7:43 pm

You are right... They are called pitot tubes. Basically those are measuring the dynamic pressure. There are also "holes" around the fuselage which are called static ports and those are measuring the static pressure. Together static ports and pitot tubes collect relevant information for instruments (airspeed, altitude, vertical speed etc...)

They are very sensitive, so protection is needed on the ground. Especially different bugs like those tubes... hard to get correct airspeed information if a bee is inside the tube for example.  Smile/happy/getting dizzy

Best Regards,
FinnWings
 
miamiair
Posts: 4249
Joined: Thu Jul 15, 2004 9:42 pm

RE: Airspeed Probes And Ground "tags"

Wed Jul 21, 2004 8:18 pm

The red tags are so the flight crew can see them on their preflight inspection. Unfortunately, some maintenance technicians cover up the static ports (the cluster of holes flush with the fuselage) with speed tape when they wash the airplane. This has resulted in the loss of two B-757's when they had un-reliable airspeed and altitude information.
Molon Labe - Proud member of SMASH
 
FinnWings
Posts: 633
Joined: Fri Oct 24, 2003 6:03 am

RE: Airspeed Probes And Ground "tags"

Wed Jul 21, 2004 8:52 pm

Unfortunately, some maintenance technicians cover up the static ports (the cluster of holes flush with the fuselage) with speed tape when they wash the airplane. This has resulted in the loss of two B-757's when they had un-reliable airspeed and altitude information.

Indeed, very sad accidents... Technicians should use bright coloured tape which is clearly visible. However, it is always responsibility of the flight crew that those pitot tubes and static ports are checked during the walkaround. If the flight crew would have done their checks properly these two accidents would have been avoided.

At my work I have seen huge differencies how well the crews of different airlines perform the walkaround. Some does it with extreme care but others might just walk around the aircraft very quickly... I have also learned how big differencies airlines might have considering the safety issues...

Best Regards,
FinnWings
 
AJ
Posts: 2304
Joined: Wed Nov 03, 1999 3:54 pm

RE: Airspeed Probes And Ground "tags"

Wed Jul 21, 2004 9:50 pm

There was an incident at Sydney airport where a Virgin Blue 737 became airborne with the pitot covers installed. As the pitot heat had burned through the front of the covers normal airspeed indications were recieved, however the whipping of the red warning tags against the fuselage forced a return to land at Sydney.
 
PPGMD
Posts: 2398
Joined: Sun Sep 30, 2001 5:39 am

RE: Airspeed Probes And Ground "tags"

Thu Jul 22, 2004 2:03 am

Here is a good site with more in-depth information on the pitot static system:
http://www.allstar.fiu.edu/aero/PSSI.htm

I also agree that MX personnel should start using bright orange or red tape, that is easier to see day and night. If you are going a night pre-flight it's next to impossible to see clear tape (what most folks use around here) over the static port. I figure that painters tape, should be water proof enough, but should also be able to come off without leaving a residue.

I should also mention that some older general aviation planes uses a flap over the pitot tube that automatically comes up as the aircraft accelerates, it's rather interesting, but they do sometimes bend either putting the flap in a permanent up position, or in most cases (well the ones that are noticed by pilots at least) in a permanent down position.

But since it's the pitot tube the pilot should notice that airspeed doesn't, as many of us say on our during take off flow, "Come alive," and simply abort the take off, and see what's wrong.
At worst, you screw up and die.
 
G4Doc2004
Posts: 120
Joined: Thu Feb 19, 2004 7:49 am

RE: Airspeed Probes And Ground "tags"

Thu Jul 22, 2004 7:30 am

Not just Pitot/Static probes are covered, but you also have TAT/SAT probes up there, as well as AOA probes and Rosemount probes, which all feed vital information to the air data computer. The covers, as FinnWings alluded to, are designed to keep moisture and other FOD out of the various ports on these probes.
"Failure to prepare is preparing to fail"--Benjamin Franklin
 
CanadianNorth
Posts: 3281
Joined: Sat Aug 24, 2002 11:41 am

RE: Airspeed Probes And Ground "tags"

Fri Jul 23, 2004 4:06 pm

Duct tape comes in a variety of colours these days....



CanadianNorth
HS-748, like a 747 but better!
 
air2gxs
Posts: 1443
Joined: Mon Jun 18, 2001 1:29 pm

RE: Airspeed Probes And Ground "tags"

Fri Jul 23, 2004 9:41 pm

We have a standing rule. If installing covers on the probes or taping ports, a log book entry will be made stating that fact.

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