Friday, 29 November 2013 16:37

737 wins again..!

B733 3

737 Wins Again

When we set about to program a particular system of the 737, we try and program it completely and accurately and then test it for bugs. Of course there are always bugs to deal with but most of the time, at least so far, we are able to work our way through them and achieve the accuracy we are striving for.

Sometimes though, after we have finished a system and moved on to other things, we will discover a bug in a system we previously believed to be complete. When this happens, then we naturally begin to question our work but maybe, just maybe, the programming is right after all and we are simply ignorant of its complete operation or made a mistake ourselves. This has happened on many an occasion where we program a system based on its engineered configuration rather than our interpretation of its operation and we found ourselves surprised about how it operates in some cases or frustrated at our lack of ability to operate it properly.

Most recently, we programmed in the manual gear releases for each landing gear, which is necessary to extend the gear when system A hydraulics are unavailable. In this situation, you have 3 pull handles on the cockpit floor that you can click on and unlock each landing gear separately. An appropriate force on the landing gear (usually gravity) will cause each gear to extend in this situation. We have this system working great.

Now before programming the manual gear unlock system, we had occasion to program in the gear configuration warning, which sounds a horn in the cockpit if the gear is not fully extended during certain flight configurations. Now in some cases, the gear horn can be silenced and in others it cannot. For more "serious" configurations, the horn will continue to sound even if you press the horn cutout button but for other situations more common during a landing scenario, it can be shut off. The logic diagram is deceptively tricky but we got it working.

So during the testing of the manual gear unlock system, we thought it might be interesting to fail system A hydraulics at a busy time, that is during an informal approach with the requisite management of the flight path, throttle and flaps as appropriate. Firstly, we failed the system A hydraulics. At flaps 10, descending below 1000' AGL and throttles back, the gear horn goes off, no surprise. We silence the gear warning horn with a press of a button and manually release the gear one at a time between making other flap, power and course adjustments.

At flaps 15 with the gear manually released but not yet fully extended, the gear warning horn goes off a 2nd time. Again, no surprise but we know we cannot cut out the gear warning in this configuration with throttles retarded and have to wait for all the gear to extend, but the horn does not silence.

As we descended towards the runway with the flaps still extending towards 'flaps 30', the gear horn is still blaring. We knew we were in a valid landing configuration: flaps 30, below 1000', throttles retarded, gear down.

Our first thought was "oh wonderful, a bug in the gear horn code we just programmed". As frustration of having to revisit "done code" and wondering what it could be set upon us, we noticed the nose gear indicator light was still red. It then hit us we forgot to release the nose gear in the course of configuring flaps and flight path and we quickly released the nose gear manually and after achieving full extension and 3 green lights, we were welcomed with sweet silence and an uneventful touchdown. The 737 was right, we were wrong. The 737 wins again. Two systems, working just as they should. Whew! A lot of damage and lawsuits averted. On to the next system!


  • Comment Link Tuesday, 28 February 2017 00:50 posted by Kenn

    Very Nice Website. Good luck

  • Comment Link Tuesday, 28 February 2017 00:49 posted by Andy

    hehe awesom Story, thanks.

  • Comment Link Sunday, 19 February 2017 00:35 posted by Lars

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  • Comment Link Saturday, 18 February 2017 07:24 posted by Stefan Sigmund

    Nice article, I really like to learn things like that. Keep us updated :)

  • Comment Link Monday, 28 December 2015 07:02 posted by Engelbert

    Please release me, let me go
    For I don't love you anymore
    To waste our lives would be a sin
    Release me and let me love again

    I have found a new love, dear
    And I will always want her near
    Her lips are warm while yours are cold
    Release me, my darling, let me go

    Please release me, let me go
    For I don't love you anymore
    To waste my life would be a sin
    So release me and let me love again

    Please release me, can't you see
    You'd be a fool to cling to me
    To live our lives would bring us pain
    So release me and let me love again

  • Comment Link Saturday, 26 December 2015 10:12 posted by Federico

    Thanks for sharing this really interesting proves the great work you are doing...and I'm sure it's so great when you realize that your work is doing what real aircraft should be

  • Comment Link Friday, 04 July 2014 23:27 posted by Vluchtplan

    Awesome, seems you are all up to 'schedule'.
    Looking forward to the end result and ... still patient ;)
    Keep up the great developments.
    Good luck!

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