This figure illustrates that an obstruction is outside of PAPI Obstacle Clearance Surface (OCS) but within PAPI light beam visual area. PAPI internal baffles are needed to block visual acquisition of obstruction outside of the OCS. (Figure from FAA Airport Visual Aid Presentation – 2014 Spring IES Conference, 5/8/14)
By Harry Lorton, P.E.
TxDOT Aviation Division Engineering Director
An issue has come up recently concerning PAPI siting and commissioning. Recently several PAPI installations have failed commissioning during the flight inspection verification. The reason for the failure was the result of objects (obstructions) being seen between the flight check aircraft and PAPI unit. It seems this issue is becoming more apparent as more and more airport PAPI’s are required to be commissioned by flight check.
When this situation occurs during commissioning, the problem is resolved by the use of internal PAPI baffles to reduce the visible portion of the PAPI light beam to block out the obstruction. This is best described by FAA AC 150/5340-30H, Chapter 7, Section 7.7, f, 7, c:
Flight check personnel will evaluate the PAPI obstacle clearance within the lateral limits of the “visible” light beam. This evaluation may exceed the standard OCS in paragraph 7.5.d(4) and Figure 80. If a larger OCS is not planned for, baffles will be required to set the limits of the OCS to 10 degrees either side of runway centerline (20 degrees total) to restrict excess horizontal light beam distribution. See AC 150/5345-28 for additional information about PAPI horizontal beam width. It is vital that personnel designing and installing the PAPI, including the project engineer, be thoroughly familiar with the requirements in FAA Order 8200.1, United States Standard Flight Inspection Manual.
It appears the FAA recognizes this issue and will be issuing an engineering brief to address this in the future. Until the FAA issues any further guidance the temporary work around is to require all new PAPI’s to be shipped from the manufacturer with adjustable-internal baffles pre-installed.
Please be aware of this issue as you design new PAPI installations.
If you have any further information or ideas concerning this please feel free to contact me at [email protected].
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