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'Not authorized at night'

New AOPA fact sheet explains instrument approach restriction policy

A pilot is planning a cross-country flight to a destination likely to have instrument meteorological conditions for the expected nighttime arrival. On reviewing the one-runway airport’s instrument approach procedures, the pilot is dismayed to discover notices to airmen advising that the IAPs are “NA at night.”
Why do some instrument approach procedures have the notation, "NA at night"?

Why are some instrument approaches not authorized at night? Can something be done to make them available on a 24-hour basis?

In many cases, a “NA at night” restriction was imposed because the FAA determined that an obstruction penetrates the visual surface area, commonly referred to as the 20:1 (twenty-to-one) slope along the runway’s extended centerline.

The visual slope area is the minimum area that must be protected if an instrument approach is to be unrestricted. The obstruction can create a flight-safety hazard, as graphically illustrated in this brief video.

The FAA’s response does not stop with a notam. Under the current policy that took effect in March, an FAA panel meets weekly to discuss the airport and its obstructions, evaluate the risk of the obstacle to flight operations, and determine a course of corrective action, as described in detail below.

AOPA, responding to numerous member inquiries concerning instrument approaches that bear “NA at night” notams, has released this new fact sheet to explain the background of the issue, the FAA’s current two-year interim policy, and plans for the future, said Rune Duke, AOPA director of airspace and air traffic.  

The typical 20:1 slope begins 200 feet before the runway threshold, and rises one foot for every 20 feet horizontally along the runway’s extended centerline. “All aircraft must have a safe path to descend and land regardless of whether they are VFR or on an instrument approach procedure,” Duke said.

Historically, the FAA dealt with penetrations of the 20:1 slope by raising approach visibility minima to one mile. In 2002, design criteria were changed to require that obstructions be marked or lit or a notam would be issued restricting the procedure.

However, airport compliance and enforcement lagged.

A process giving airports three years to become compliant (and gain access to promised grant funds to pay for solutions, in some cases) was created, but the policy was rescinded in 2010.

“In 2013, the FAA, AOPA, and other industry stakeholders met as part of the Visual Approach Surface Task Group to offer recommendations as to what the new guidance should be for a proactive system and a risk-based enforcement philosophy,” Duke explained. “The subsequent policy, which took effect in 2014, allowed sufficient time for the airport operator to verify the obstacle and, if it was verified to be valid, more time to mitigate it by removal, lowering, or another method.”

Obstructions were designated low risk if the obstruction penetrated the 20:1 slope by three feet or less; medium risk if between three and 11 feet; high risk if the penetration exceeded 11 feet. A high-risk obstruction required immediate restriction of the procedure. All risk levels required a compliance plan be submitted in no later than 30 days, and mitigation by designated deadlines.

The FAA also stepped up its outreach to airport sponsors to raise awareness of the slope-penetrating-obstruction hazard.

When that interim policy guidance expired in early 2016, an FAA review of 3,002 airports and 16,518 instrument approaches showed that during the two years the interim policy was in effect, more than 900 airports and about 2,000 procedures were limited by a 20:1 obstacle. Of those, 565 airports eventually removed or mitigated the obstruction.

The FAA presented its new interim policy and enforcement philosophy in March, retaining the AOPA-supported risk-based approach.

“The FAA has committed to maintaining that policy into the future.’ Duke said.  

As new 20:1 obstructions are identified by the FAA and validated by the airport, they will be submitted to the FAA Flight Standards Procedure Review Board, which meets weekly and includes representatives from the Flight Standards Service, Operations Support Group Flight Procedures teams, Airport Standards Division, and Mission Support Services.

The board will discuss the airport and the obstruction’s penetration risk (for example, its location, height, type of object, whether it is lighted) and may grant a restricted waiver to complement an airport compliance plan, or initiate corrective action with a notam or by amending the procedure, Duke said.

Steve Szukala, FAA manager of the Instrument Flight Procedures Group, noted that the new policy “has not been signed but we are operating as if it was. Looking at the data statistically since January, it looks like we have around a 1-percent potential non-compliance with the key word being potential. In the first two years we were around 60-percent non-compliance. Looks like the pain from the first two years of getting obstructions cleared has truly made a safer National Airspace System.”

The FAA hopes that when the two-year effective term of the new interim policy expires, airport operators “will be aggressive and better educated regarding obstructions so there will be fewer penetrations identified.”

The new policy also will allow a better understanding of why obstructions are still being identified, and the most effective way to prevent future penetrations, Duke said.

 “AOPA will remain involved with advocacy from a flight procedure design and airport perspective,” he added.

Dan Namowitz

Dan Namowitz

Dan Namowitz has been writing for AOPA in a variety of capacities since 1991. He has been a flight instructor since 1990 and is a 35-year AOPA member.
Topics: Airspace, Navigation, Technique

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