Upaved Strip Kit. 「The optional Upaved Strip Kit was made available for the 737-100/200 from Feb 1969. It allowed aircraft to operate from gravel, dirt or grass strips. At its peak of operation, 737s were making over 2000 movements a year from unpaved runways.」 SEE ALSO: https://en.wikipedia.org/wiki/Gravelkit http://www.b737.org.uk/unpavedstripkit.htm