Landing radar reasonableness

FC4/Chief, GNC SectionFEB 20 196868-FM-T-35FM/Deputy ChiefLanding radar reasonableness

1. Here is another request for information—this time dealing with landing radar reasonableness. The basic question is how well can the crew evaluate the quality of the landing radar data from the displays available to them prior to permitting the data to be accepted by the PNGCS? For example, is it possible for it to read out the wrong altitude but give every indication that it is performing in a perfectly normal manner? Or can we be confident that if we see the displays moving smoothly that the data is probably right?

2. The thing I am afraid of is that the altitude it indicates may be quite different than the navigated PNGCS displayed value, since I would not be surprised if the latter could be substantially in error due to errors in the initialization, terrain uncertainty, navigation error, etc. The point is it sure would be nice to be able to tell if the radar was working even in the face of a large altitude difference, since it is in that case we need the radar data the most.