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Pitot heaters . . . warn or not, that IS the question

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Aug 10, 2009 9:48 am Post subject: Pitot heaters . . . warn or not, that IS the question

At 12:13 PM 8/8/2009, you wrote:

Bob..



The reason I asked is that I was looking at the events surrounding 

Air France AF447 (A330) in mid atlantic.



I saw that AF and Airbus have been dinking around with pitot tubes, 

and have been through three types (Rosemount, Goodrich, Thales 

C16195AA so far, and were about to install the fourth type (Thales 

C16195BA) just before the accident.



I was trying to envisage what can go wrong with a pitot tube...it's a 

brutally simple device, and I came up with three scenarios:



1...Physical damage (Hail, catering trucks).

2...Insufficient heating.

3...Defective heaters.



As far as I can tell, there is no attempt made to monitor heater 

performance, either by monitoring input power or by measuring 

temperature., so I wondered if heating could be simply inadequate.  I 

came up blank when I tried to research the actual heater wattages.



    Heating is almost never "inadequate" to the design

    goals in place when the tube is originally installed

    and qualified on that airplane. Problem is that

    design goals and mother nature's ability to paste your

    airplane with a layer of ice are not necessarily

    in synch.

Incidentally...I believe that the primary causative factor was the 

crew's decision (or non-decision??) to continue their planned flight 

path despite the fact that it went directly through a monster 

thunderstorm.  The thing that is open to conjecture is the sequence 

of events after that.



    Hmmmm . . . The idea that an airplane becomes at

    risk for unplanned arrival with the earth because

    IAS/TAS values are suddenly "unknown" is a bit of

    a stretch. But this assumes that some automatic flight

    control system doesn't react and starts

    fiddling with the airplane's configuration. In

    the case I worked, the manufacturer wrote some specific

    procedures for flying based on AOA in the rare cases

    that airspeed becomes available. In any case, there

    was no known risk that the event would occur during approach

    to landing but even then, a landing using AOA and

    windage corrected, GPS ground speed was quite possible

    and practical.



    If the heater is drawing current, then it's working

    as designed. The Hawker-Beechcraft products nearly

    all feature some form of heater current detection

    to drive a light. This is spelled out as a requirement

    in paragraph 1326 of both FAR Part 23 and Part 25



----------------------



Sec. 23.1326  Pitot heat indication systems.



If a flight instrument pitot heating system is installed to meet the

requirements specified in Sec. 23.1323(d), an indication system must be

provided to indicate to the flight crew when that pitot heating system is not

operating. The indication system must comply with the following requirements:



(a) The indication provided must incorporate an amber light that is in

     clear view of a flightcrew member.



(b) The indication provided must be designed to alert the flight crew if

     either of the following conditions exist:



     (1) The pitot heating system is switched "off."



     (2) The pitot heating system is switched "on" and any pitot tube heating

         element is inoperative.



[Amdt. 23-49, 61 FR 5169, Feb. 9, 1996]

----------------------



   If you'd like to include a similar system in your

   heated pitot planning see:



http://www.aeroelectric.com/articles/Failure_Detection_and_Annunciation.pdf



        Bob . . .



         ---------------------------------------

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

         ---------------------------------------

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BobsV35B(at)aol.com
Guest

Posted: Mon Aug 10, 2009 1:19 pm Post subject: Pitot heaters . . . warn or not, that IS the question

Good Afternoon All,

  

 The following passage was in a message to which 'Lectric Bob responded, but  I was not able to discern the author.

  

 "Incidentally...I believe that the primary causative factor was the  

crew's decision (or non-decision??) to continue their planned flight  

path despite the fact that it went directly through a monster  

thunderstorm.  The thing that is open to conjecture is the sequence  

of events after that."

  

 I wish to respectfully disagree. 

  

 Staying out of severe weather is always a good idea, but airplanes have  been flying successfully through such extreme storms as long as we have been  flying IFR. As long as the crew has adequate instrumentation and the requisite  skills to use it the airplane will hang together. Back before we had as much  deviation capability, airplanes were accidentally flown through extreme  hurricanes and even tornados. Some of the airplanes needed serious repair  following those excursions, but they did bring their payload safely back to  mother earth. 

  

 It is certainly wise to avoid those conditions, but the airplane will  handle it adequately even though it may be damaged and the passengers most  assuredly would not have a very pleasant ride.

  

 I think you will find an effort by the applicable certification entities  to blame the crew for flight where they should not have been, but I think the  true story is that the crew either did not have the required instrumentation  available to them or that they were not properly trained in the use of what was  available. 

  

 Blaming the weather is a cop out to avoid design or  training responsibility.

  

 Happy Skies,

  

 Old Bob

 AKA

 Bob Siegfried

 Stearman N3977A

 LL22

 Downers Grove, Illinois

 



 

  [quote][b]

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