Re: External inspection

Date:         13 Feb 99 02:26:06 
From:         Larry Stone <lstone@wwa.com>
References:   1
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On 1 Feb 1999, JF Mezei wrote:

> > It wouldn't appear to be inop.  If the static  pressure trapped inside
> > the system was the same as the current outside static pressure,
> > everything would appear normal.  You would only notice an invalid
> > reading when the static pressure changes from what is trapped inside
> > the system.
>
> I do not understand. If the static pressure trapped inside the system
> were enough to show a V1 speed on the pilot's gauges, shouldn't pilots
> have noticed that the gauges were reading V1 while the plane was iddle?
> If looking at the needle move until it reaches V1 is partof the
> responsabilities of one of the 2 pilots, shouldn't that pilot not have
> noticed that the needle was not moving?

Read the comment you replied to (quoted above). An airspeed indicator
indication is a function of the static pressure and the ram-air pressure
from the pitot tube. As long as the trapped static pressure equals the
current outside pressure, then the airspeed indicates correctly (which was
have been the case while the plane was on the ground). It's only when the
outside pressure is different from the trapped pressure that you have an
indication error.

Note that this is very different from when static pressure is OK and the
pitot tube is blocked (trapped ram-air pressure) in which case the
airspeed indicator acts like an altimeter.

-- Larry Stone
   lstone@wwa.com
   http://www.wwa.com/~lstone/