Boeing 737s can't land facing west (FAA via Clive D.W. Feather, R 31 56) The FAA received reports earlier this year of three incidents of display electronic unit (DEU) software errors on Model 737 NG airplanes ying into runway PABR in Barrow, Alaska. All six display units (DUs) blanked with a selected instru- ment approach to a runway with a 270-degree true heading, and all six DUs stayed blank until a di erent runway was selected. [...] The investigation revealed that the problem occurs when this combination of software is installed and a susceptible runway with a 270-degree true heading is selected for instrument approach. Not all runways with a 270-degree true heading are susceptible; only seven runways worldwide, as identi ed in this AD, have latitude and longitude values that cause the blanking behavior. (Note that this is all 6 dis- plays on each plane, not 2 displays on each of three planes.) (R 31 54). [More items later on polar coordinates, tangent of 90 and 270 being plus-minus in nity, etc. (R 31 56,57)