Memorandum - NHTSA

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Jacking Prevention (S6.8) - The control system or inherent lift design should be such that
"jacking" is prevented. This test is to be conducted unloaded and loaded 272 kg mass (600 lbs .).
Jacking is the support or lifting of the bus by the wheelchair lift when the platform is power
driven to the ground level. This can cause failure, breakage, or permanent deformation to part ;
of the lift and could cause jamming and render the lift inoperable when at a bus stop. Some
active lifts employ gravity to lower the lift platform in cases where jacking is not a problem. �'or
passive lifts, where power is normally applied to lower the lift, jacking could create a problem It
is believed that power-down lifts already employ a contact switch to detect ground contact and to
override lift operation. The prevention of jacking is consistent with the FTA-sponsored
guidelines and would not apply to the manual backup mode of lift operation. Jacking was not
addressed by the Access Board. It is believed that all commercial and personal lift products
already comply with this requirement. In the SNPRM the agency also proposed an anti-crush
interlock (S5.10.2.7) that would stop the lift's motion if the 3 primary edges of the lift platfom L
contacts an object anywhere along the downward vertical travel path. The agency anticipated
that the anti-crush interlock would be based on the anti-jacking sensor, but modified in terms of
sensitivity and area. That is, it would be sensitive enough to not crush a baby carriage or a
child's foot or leg once contact is made and the sensing area would include the three primary
sides of the lift (excluding the side next to the vehicle. Anti-crush interlock requirements werc:
not included in the Final Rule due to cost and function intricacies.