The DHC-8-400 (and possibly other DHC-8 variants) has (or, at least, had in late 2007, according to Appendix G of this AAR) a warning light labelled “TOUCHED RUNWAY”.
The extract of the DHC-8-400’s QRH quoted in Appendix G of the aforementioned AAR mentions this warning light at the end of the landing-gear abnormal-procedures section, and says what to do if the light illuminates, but not what the light actually indicates:
- Do Not Start APU
- Advice [sic] ATC for Runway Inspection
Note: Continued flight operations require maintenance approval.
The landing gear of a DHC-8-400 (or, indeed, of any aircraft so equipped) routinely touches the runway, and the ramp, and the taxiways, and the hangar floor, all the time during routine operations - indeed, touching the ground (including, but not limited to, the runway) is literally the primary, and very nearly the entire, purpose of landing gear! So what does the “TOUCHED RUNWAY” warning light indicate that is severe enough to warrant possibly grounding the airplane?