At NWA our DC-9's had a lever that slid over and was safety wired that limited it to 30 degrees and you could break that safety wire and slide that lever to the right and go to flaps 40 if needed.

 

Was that in the "half Nelson" and "full Nelson" era of slat/flap and speed brake use?

GF

 

The hush kitted DC-8 that I flew had the same restriction based on noise. We got a temporary lifting when we flew hurrican relief to St. Thomas.

 

Many modern aircraft can land with multiple flap settings as well. The E170/190 family is certified for normal landings at flap settings of both 5 and FULL. Most operators typically use 5 for landing (a slightly higher approach speed and longer landing roll, while making less noise and burning less fuel, plus easier to handle in crosswinds), but FULL is available when desired or required. Republic, for example, takes the E175 to KEYW, which requires flaps FULL landings at all but the lightest weights due to the short runway.

The A320 family is certified to land at both Config 3 and Config FULL as well. Again, 3 results in a slightly higher approach speed and landing distance, but with the benefit of less fuel burn and noise.

Also, the lesser flap settings can improve handling qualities on windy days ... especially gusts and/or crosswinds.