Adding on a bit more airspeed
on the approach "for safety" can often be distinctly dangerous. reproduced from GASCO
Watching single engine
aeroplanes landing at a large airport can be really quite depressing
sometimes. All too often they arrive over the threshold far too fast and
eventually make contact with the runway some 500 m or more into it after
an extended and porpoising passage at varying heights above the surface
while the pilot waits for the excessive speed to decay. Sometimes they do
not wait long enough and allow the aircraft to touch down nosewheel first,
which is never a good idea. Sometimes the pilot prolongs this anxious
expedition just above the runway even further by failing to deploy
sufficient flap or forgetting to close the throttle fully. Add in a bit of
a crosswind and the antics of the overstressed pilot during this drawn out
and apprehensive journey from threshold to touch down can be quite eye
catching.
For single engine aeroplanes,
the practice of adding on a bit extra airspeed "for safety" is generally a
bad idea. It imposes extra demands on the pilot at the round out, it
invites "wheelbarrowing", caused by touching down too soon and it tends to
form a very bad habit that may become dangerous when the pilot has to land
on a relatively short runway.
the wheelbarrow
The correct approach speed is
probably specified in the aircraft's Pilot's Operating Handbook (POH) and
this speed, not five knots more, is the speed you should aim for. The more
comprehensive POH will offer a range of speeds depending upon
configurations and how close to Maximum All Up Weight the aircraft happens
to be. If the POH gives no guidance, the classic approach speed for an
aeroplane is 1.3 times the stalling speed, and by `stalling speed' is
meant the stalling speed in the approach configuration and at the actual
weight for that particular approach. A small increase in approach speed
may be specified in the POH for gusty conditions and some increase in the
approach airspeed here is sensible, but only in moderation.
A common recommendation seems
to be to add on to the normal approach speed half of the amount that the
gusts are exceeding the general wind speed at the time. Thus, if the
reported wind at the threshold is 15 KTS, gusting 25 KTS, the
recommendation would suggest an addition of 5 KTS to your approach speed.
This increase should however, only apply to the headwind component of the
surface wind. Unless the POH specifically recommends otherwise, there is
no need to add anything for a crosswind.
Having established the
aeroplane at the correct approach speed and configuration, in trim, the
POH may recommend a lower `threshold' speed (sometimes called VREF
although that is the intended speed for a commercial aeroplane at a height
of 50 feet above the threshold). Any deceleration required should take
place in the final stages of the approach.
After crossing the threshold,
the speed should be allowed to reduce during the `round out' or `flare'.
This in essence is a period of level flight just above the runway, in
which the pilot progressively adjusts the pitch attitude as the speed
reduces, until the correct landing attitude has been achieved. He should
then hold that attitude to allow the aeroplane to settle onto the runway.
If the correct threshold speed has been achieved, float is kept to a
minimum and the aeroplane will settle comfortably shortly after crossing
the threshold.
Just the right speed for touch down for a single engine aeroplane such as
this Pulsar. More speed means more difficulty
You may have used a
takeoff and landing performance calculator thinking that it is good for
any landing speed.
I am afraid that calculating whether you will have sufficient runway for
your landing will be useful only if you stick to the correct approach
speed. If you commonly adopt an approach speed higher than the
recommendation and then touch down 500 m into the runway, you had better
either mend your ways or add 500 m on to the "landing distance required"
calculation.
If you let the speed get too low on an asymmetric approach in many twins,
and then try to recover by increasing the power on the good engine, the
consequences can easily be fatal
A recent accident report
demonstrated convincingly what might happen if the false idea that a
higher approach speed leads to greater safety is adopted. The owner pilot
of a relatively new Cirrus SR22 had to land at a strange airfield. In his
report he says, I knew I was going to have to land a little faster than
normal because of gusty winds. We do not know how much extra he added but
his report continues, ...nearing landing and at treetop level ... I
encountered a wind gust ... that made me add power.
When I had recovered, I had
picked up about 5-10 KTS of more airspeed. The report then describes how,
following touch down, the pilot was unable to stop in time and ended up in
a fence with a substantially damaged aeroplane. While I may have
misunderstood what went on here, it does seem to me that what was at the
heart of the problem was the concept that more power and more speed were
always the required answer to a sudden gust. Of course, if the pilot
encountered a lull in the wind speed, sensed the approach of a stall
and/or saw that the airspeed had reduced, then more power and more speed
would have been the appropriate response.
But he had already added some
extra speed and a gust could just as easily have added even more to his
airspeed as reduced it. The essential point is that the pilot needed to be
practised in slow flying (as we all need to be) to attempt a landing in
gusty conditions. He had already added something to his approach speed and
what he needed to do beyond that was to be extra sensitive to airspeed and
the feel of the aircraft and to make power and pitch adjustments
appropriate to what the ASI and the feel were telling him. If these told
him that the gust had increased his airspeed, then an increase in power
would have been quite the wrong response.
Based upon the limited
information available to me about this American accident, I cannot be sure
whether the pilot was actually at fault in any particular; he probably
wishes now that he had thrown away this taxing first approach and gone
around for a less stressful second attempt.
Reggie Bender always adds another 10 KTS, just in case
Never forget that during any
approach or any other time when flying slowly and close to the ground,
your airspeed is always the vital factor and whatever the other
distractions, you must monitor the airspeed constantly. Let the airspeed
get too low, and you may stall and spin. Let it get too high and you will
face all the problems described above. The only safe policy is to adopt a
speed that complies with the POH or, failing that, the classic rules
described. Having chosen your target speed you must then make quite sure
that, regardless of any distractions that may arise, you continue to aim
for that speed. That will match the interests of the wife and kids far
more closely than automatically adding on another five knots.
