L-1011 Flight Controls: DLC and Glide Slope (27-41/44)

The image above shows the aircraft on approach path. DLC spoilers 1, 2, 3 and 4L and 4R are up to null position of approximately 10º up. The spoilers will operate up to 20º or close to 0º from the null position with session of Pilot or Autopilot pitch inputs. 

Once panels have moved to a position from the 10º null position they drift back to the null position ready for the next excursion.

If the aircraft moves above the glide slope, DLC commands spoilers 1, 2, 3 and 4 open to 20º reducing approximately 10% of lift. 400,000 lb. of weight results in a -40,000 lb. of lift reduction. The airplane returns to approach path with only a minor pitch change. This provides increased passenger comfort. 

If the aircraft has drifted below the glide slope, pitch input causes the close the increasing lift and the aircraft flies back into approach path with only minor pitch changes. DLC serves one additional important function: its use reduces the size of the landing touchdown zone scatter. Thereby improving category III autoland precision.

The image above shows the Surface Position Indicator with DLC spoilers 4 and right 2 indices traveling also the speed brake lever traveling in the DLC range in response to pilot commanded stabilizer movements.

DLC automatically disengages under any one or all of the following conditions:

1. Stall Warning 
2. Go-Around Switch Activated
3. Any two Throttles Advanced 
4. Flaps Retracted less than 30º
5. Pilot-mnaual Override of Speed Brake Lever
6. Pilot Assist Disable Switch Pressed
7. System Failures