View Full Version : Autoland wind limitations
B737NG_Pilot
1st Oct 2023, 01:35
Why do we have a head wind limitation for auto land ?
Why do we have a head wind limitation for auto land ?
It's a very long time since I was involved with autoland flight test and certification. My recollection is that the systems I worked on were limited to the maximum values that were actually demonstrated during certification flight test. It's surprisingly hard to find suitable airports with the winds that one would like to have for certification demonstration.
ImbracableCrunk
1st Oct 2023, 12:07
Probably the same reason we have a 20,000' flap limitation, "That's where we stopped testing, so that's your limit."
I said it had been a long time since I was involved with autoland development but I was curious enough to dig a bit into those distant memories. AC 120-28 is the "bible" for autoland systems development. The current version is D and it, and the related appendices, can be found here - https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentid/22750
Autoland certification uses simulation to demonstrate performance under a huge range of conditions. The flight test program has to produce sufficient data to show that the performance of the aircraft matches the performance of the simulation. One of the inputs to the simulation is the wind model that is defined in Appendix 4. If my interpretation is correct that wind model does not produce headwinds that exceed about 26 kts.
It seems likely that the autoland wind limits are set by the wind model.
I found the Type Inspection Authorization for the DC-9 Series 80 autoland system. Included in the required conditions for the aircraft demonstration:
Conduct 100 autolands with the following wind component criteria:
1. Headwinds - At least 10% at 12.5 knots or higher with a minimum of 2 landings at 20 knots or higher.
2. Crosswinds - At least 10% at 7.5 knots or higher with a minimum of 2 landings at 12 knots or higher.
3. Tailwinds - At least 2 landings at 5 knots or higher.
It was finding these TIA required wind conditions that was difficult, not finding certification limit winds.
B737NG_Pilot
2nd Oct 2023, 03:20
Thank you EXDAC... Makes sense
Amadis of Gaul
11th Oct 2023, 09:10
Why do we have a head wind limitation for auto land ?
Who is "we" and what airplane are "we" flying this week?
Capt Fathom
11th Oct 2023, 11:06
Probably the same reason we have a 20,000' flap limitation, "That's where we stopped testing, so that's your limit."
Mach number limitation.