Growler,
The approach speed for a C152 is around ‘55-65 KIAS with flaps and reducing to 54 KIAS at fifty feet’ (Model 152 Information Manual). Given that a stabilized approach is achieved with a rate of descent of about 500 feet per minute, this equates to some five degrees gradient – steeper when a head wind is considered. Assuming that a threshold crossing height of fifty feet is achieved, touchdown will occur at a point 600 feet or 182 metres from the threshold. Other factors applicable to light aircraft pilots include the possibility of engine failure and approach obstacles existing on many GA runways particularly those surveyed just 150 metres from the threshold.
Most approach aids such as PAPI, T-VASIS and ILS achieve a three degree glideslope. Given that a performance type will approach at or above a Vref speed double the approach speed of the C152 but still stabilized at about 500 feet per minute the ‘aided’ glidepath will work. A three degree touch down zone will intersect the runway based on 50ft TCH precisely 1000 feet from the threshold – hence the markers.
Why would one wish to train a student in a C152 or similar to achieve a three degree glidepath when such is outside the recommendations of the POH? Airlines have the right to insist of achieving PAPI & G/S – flying schools have the right to insist upon achieving the criteria prescribed in the POH and that will probably include ignoring the PAPI or T-VASIS in day VFR operations.
Fully agree with your comments on the carburetor heat. Should be selected to cold when landing is assured. Engine life will be considerably extended if the ingestion of abrasive dust particles is avoided by filtering intake air.
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dragchute
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