Off another forum. Interesting process of TERPS criteria.
http://www.airlinepilotforums.com/safety/76529-ups...
IAP/PAPI vs TROUBLE T
DISCLAIMER: I haven’t seen this analysis depicted elsewhere to date, so here I go…Without (a) speculating into any details of the fatal incident which occurred at KBHM last week or (b) referring to any proprietary publications, practices, or property of any non-tax-funded entity, I would like to expand on my understanding of a significant issue. This interpretation comes from quite a few years of instruction (given and received) in military and civilian multi-engine aircraft operations and instrument flying. You may think this issue directly relates to the recent KBHM incident, but I am expanding on it independent of that. I am trying to document my understandings with hopes that others can correct any errors and/or help better explain how these issues may impact flying safe. Finally, please keep in mind that I am a pilot and not a TERPS certified engineer, but I think we all should hear from one.
SUMARY
Obstacle information for the area north of BHM RW18 over-laid with visual AND instrument approach path information do NOT depict safe vertical clearance of obstacles. Comparing actual vs. published approach path settings (on PAPIs for example) does nothing for ensuring that the resulting path will adequately guide a pilot clear of obstacles – that is merely an accuracy check against a book. There appears to be an error with FAA provided information given to pilots and that information needs to be changed OR obstacles/terrain need to be lowered OR approach paths, visual AND instrument, need to be altered to allow for safe vertical clearance of obstacles.
EXPANDED INFO
Source documents: Current FAA/NACO IAP for LOC 18 and ODP for KBHM; USAF flying regulations (real exciting – and available online)
1. In order to determine obstacle information for landing on RW 18, one can look at climb restrictions and data for departing RW 36. This is a somewhat counterintuitive idea that stems from the fact that if an airfield doesn’t have a published approach procedure, USAF pilots can’t depart it under IFR…it’s either TERPS validated both in and out of the field or it hasn’t been TERPS at all, and if it’s the former, all obstacle data should be accurate. Also, this is NOT a standard practice NOR procedure as it is assumed approach procedures and airfield approach lights are in place to safely avoid all obstacles in applicable flight path; it is a semi-advanced Instrument Instructor technique to examine fields surrounded by terrain to, if for nothing else, validate which direction from the airport has the most/least restrictive path in and out.
2. The required climb gradient of 420’/nm to 1000M can be used to determine the Obstacle Clearance Surface (OCS). The OCS line connects a starting point over the end of the runway with the peak of the most controlling obstacle or terrain through the altitude limit indicated.
2a. The OCS line must be assumed to start at ‘screen height’ or distance above the end of the runway of 35’ because the airfield analysis/approach procedures are developed by the FAA for military and civilian use (airports used only for specific branches of the military do not use a screen height, which provides more of a margin of safety for clearing obstacles).
2b. 48’/nm must be subtracted (it is the standard buffer used in published climb gradients per source document).
2c. The resulting 372’/nm forms the OCS line (high school math on 372’/6076’ derives a 3.5 deg angle…steeper than the 3.28 deg angle of the Precision Approach Path Indicator AND the 3.28 deg angle of the PAPI lights AND the path expected to be displayed on aircraft vertical navigation or profile indication systems.
3. PAPI lights alone are supposed to provide obstacle clearance within 3.5nm of the landing runway and a TERPS’ed approach procedure should do the same from the point one is established on the procedure until you get to minimums at take over visual navigation to the runway (in this case aided only by the aforementioned PAPIs). The instrument approach procedure should comply with Required Obstacle Clearance standards (starting at 250’ clearance above obstacles and tapering down to a lower but safe amount of clearance as the aircraft nears the runway). Given the data derived below using basic trigonometry, I don’t see how the FAA provided data can be construed as the most safe or compliant.
[IMG][/IMG]
CONCLUSION: According to my calculations, there appears to be an error with FAA provided information given to pilots and that information needs to be changed OR obstacles/terrain need to be lowered OR approach paths, visual and instrument, need to be altered (increased descent angle and or higher runway crossing height) to allow for safe vertical clearance of obstacles. If my calculations are off, I think they are close enough to validate imposing restrictions on the use of ANY vertical path guidance for transport category aircraft to RW 18 in anything but day/VMC conditions.
NOTE: Several years back, I nearly put two student pilots to sleep with the concept outlined in step 1 above during pre-flight. We/I didn’t work through the data crunching and plotting process, but needless to say their eyes were opened when I took them into KBHM to get a close-up view of the terrain to the north. It was day/vmc in the overhead/closed traffic pattern, but we all learned why KBHM was highlighted (with the likes of Eagle County and Jackson Hole) in the USAF instrument flying regulations. I wish I had crunched these numbers and challenged someone up the flagpole…