Re: Korean Air 801 crashed on approach to Guam

Date:         29 Aug 97 00:53:42 
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
References:   1 2 3
Followups:    1 2
Next article
View raw article
  or MIME structure

In article <airliners.1997.1773@ohare.Chicago.COM> (C. Marin Faure) writes:
>Other posts have done a good job describing the function of the ILS and
>glide slope.  When I was obtaining my instrument rating at Honolulu
>International back in the 1970s, I shot full ILS approaches and
>localizer-only appproaches, mostly at night as that proved the easiest
>time to schedule lessons.  The Cessna 206 I was flying did not have an
>autopilot so all my approaches were flown by hand.  If anything, the
>localizer approach was easier as I merely had to descend in steps to
>specific altitudes at specific points and then level off until reaching
>the next point of descent which was marked either by a marker beacon
>(radio signal, not a light) or crossing a VOR (another type of radio
>signal).  The rate of descent didn't matter as long as you didn't descend
>before reaching the descent point or descend below the next specified
>altitude.  The full ILS with glide slope was a little harder (without an
>autopilot) simply because you had to maintain a specific rate of descent
>throughout the approach.  But both approach types are easily mastered by a
>competent student instrument pilot with only a hundred or so hours of
>total flight time.

And how many times does the student get to fly them?

A typical 747 crew is going to average 60-80 hours of flight time a month.
The typical flight will be 10-13 hours.  That is going to be 4-8 landings
a month.  Divide that by two, you have the actual "pilot flying"
responsibilities.  With ultra-long-haul flying, the situation is probably
worse than this.  And each of those landings will typically be made into
a modern, well-equipped airport.  On the other hand, pilots for carriers like
Southwest can do 6-8 landings a *day*.

Most carriers do not augment this lack of experience with supplemental
training.  Most rely upon the high experience levels of the crew being
a sufficient safety net.  You lose this, of course, when you start dealing
with ab initio carriers.  This is why some ab initio carriers actually
expend quite a bit of effort to maintain currency.  It was Cathay Pacific,
if memory serves, that was going to buy a 747-400 just to shoot touch-and
goes, at one point.

Non-precision approaches--particularly NDB approaches--have been decried by
the Air Line Pilots Association and other groups as being incompatible
with safety in commercial transport operations, since at least the 1950s.

Non-precision approaches are not in of themselves unsafe, but they do create
certain human demands which are difficult to compensate for.  Many CFIT
incidents occur when pilots have to "go back to basics."  At least a few
accidents have been caused by crews performing procedure turns in the wrong
direction; they are forced to revert to these procedures when radar and
other modern accessories aren't available.  And remember, you're forced
to revert to these rusty skills in bad weather.

In this case, you lose a few safety features.  You lose vertical guidance.
Suppose you don't have your altimeter set correctly.  As you DIVE to maintain
the minimum descent altitude, which is typically only a few hundred feet
above field elevation, you don't have much time to react to procedural
errors.  On the other hand, an ILS approach usually starts with level
flight twice as high as that.  You intercept a glide slope, and have several
cross-checks as to altitude and signal integrity.

None of this necessarily has any bearing on the latest Korean Airlines
crash, but you do need to keep in mind that as a GA pilot, you will be
exposed to types of flying and to procedures that some airline pilots may
have never had to deal with.

Robert Dorsett                         Moderator, sci.aeronautics.simulation               

           "Bother," said Pooh when his engine quit on take-off.