Safe and successful instrument flight is in the details. What does it mean when a procedure is marked as “not authorized?” Doesn’t the controller protect you by refusing to clear you for an unauthorized procedure?
It’s your responsibility as pilot-in-command to be aware of the limitations on approach procedures, to avoid asking for an unauthorized approach, and to refuse a clearance if it includes a procedure that’s not authorized. Air Traffic Control’s guidance is to clear you for any procedure you request as long as there is no conflict with other IFR aircraft. What sorts of procedures may be “not authorized” for an instrument approach? How will you find out a procedure is not authorized, so you’ll know not to request it or attempt to fly the procedure?
Symbology
Most “not authorized” instrument procedures are identified in textual notes on the approach chart. There is no specific symbol to jump out and alert you. You must read the notes at the top of the chart and look for the notation “NA” – for example, “Circling to Rwy 5-23 NA at night.”
Here are some limitations that may apply to an instrument approach.
NA at Night
“Occasionally, operations at an airport may be limited at night,” wrote James E. Terpstra, now retired Senior Corporate Vice President at Jeppesen. “Because runway lighting is required for approval of night instrument operations, some approaches are authorized only during the day. In some cases, the mountainous terrain around an airport is so significant that some night operations may be limited or not authorized at night.”
Circling NA
If terrain or obstacles are near the airport, straight-in approaches may be authorized but circle-to-landprocedures may not. A variation on this theme is when an obstacle exists on one side of the airport but not others, and circling is not authorized if it takes the airplane near that obstacle. In this case, you may see a note that says, “Circling NW NA,” for example, if any circling maneuver that would take the airplane northwest of the airport puts it in conflict with the obstacle. Or “Circling to Rwy 15 NA” if maneuvering from the final approach course for the procedures being flown cannot safely end with a circle-to-land maneuver to Rwy 15.
Circling NA at Night
It may be that obstacles or terrain permit circling in daylight conditions (even in poor weather that requires a circle-to-land maneuver), but the obstruction is not lighted, so attempting the circle maneuver at night is hazardous. In this case, a note such as “Circling to Rwy 5-23 NA at night” provides you with this warning.
Straight-In Minimums NA at Night
At first glance, this may seem odd. It sounds like it means straight-in procedures are not authorized, but circling maneuvers are. That seems backwards. What this notation is really saying, however, is that you must use the circling minimums value to define MDA, DH or DA even if you’re flying a straight-in approach – a straight-in procedure is authorized, but you must use the higher circling minimums. This is usually because the runway has limited lighting that does not completely prevent the use of the procedure at night but that requires you to be more conservative about flying it after dark.
Temperature-Limited GPS Approaches
This one is a little more esoteric but no less vital. Procedures that use GPS to generate an electronic glidepath through Baro-VNAV may not provide obstacle clearance below the procedure’s Minimum Descent Altitude (MDA). What is Baro-VNAV? The FAA tells us:
Baro-VNAV is an RNAV [GPS] system which uses barometric altitude information from the aircraft’s altimeter to compute vertical guidance for the pilot. The specified vertical path is typically computed between two waypoints or an angle from a single way point. When using baro-VNAV guidance, the pilots should check for any temperature limitations which may result in approach restrictions.
This is why IFR approach-cer-tified GPSs prompt the pilot to enter the current altimeter setting into the box before loading an approach. The GPS uses its terrain database to calculate and display an electronic glidepath using barometrically derived altitude information. But the FAA warns there may be temperature limitations on Baro-VNAV approaches. The Aeronautical Information Manual (AIM) tells us:
Hot and Cold Temperature Limitations. A minimum and maximum temperature limitation is published on procedures which authorize Baro-VNAV operation. These temperatures represent the airport temperature above or below which Baro-VNAV is not authorized to LNAV/VNAV minimums. As an example, the limitation will read: “Uncompensated Baro-VNAV NA below -8°C (+18°F) or above 47°C (117°F).” This information will be found in the upper left hand box of the pilot briefing. When the temperature is above the high temperature or below the low temperature limit, Baro-VNAV may be used to provide a stabilized descent to the LNAV MDA; however, extra caution should be used in the visual segment to ensure a vertical correction is not required. If the VGSI is aligned with the published glidepath, and the aircraft instruments indicate on glidepath, an above or below glidepath indication on the VGSI may indicate that temperature error is causing deviations to the glidepath. These deviations should be considered if the approach is continued below the MDA.
NOTE: Many systems which apply Baro-VNAV temperature compensation only correct for cold temperature. In this case, the high temperature limitation still applies. Also, temperature compensation may require activation by maintenance personnel during installation in order to be functional, even though the system has the feature. Some systems may have a temperature correction capability, but correct the Baro-altimeter all the time, rather than just on the final, which would create conflicts with other aircraft if the feature were activated. Pilots should be aware of compensation capabilities of the system prior to disregarding the temperature limitations.
There’s good news for pilots of WAAS GPS-equipped aircraft:
NOTE: Temperature limitations do not apply to flying the LNAV/VNAV line of minima using approach certified WAAS receivers when LPV or LNAV/VNAV are annunciated to be available.
In other words, if you’re flying a GPS approach using a non-WAAS approach-certified GPS, watch for limitations on the use of the advisory glidepath in very hot or very cold conditions. If you’re using a WAAS GPS or the temperatures are not extreme, you’ll quickly dismiss this warning when you see it.
Other NAs
This is not an all-inclusive list of the procedures that may not be authorized for a given approach. Read the notes thoroughly as you brief for the approach. Remember, your success is in the details.
Won’t Controllers Protect Me?
Controllers won’t prevent you from trying to fly an unauthorized approach. According to the FAA’s guidance to controllers in Air Traffic Organization Policy JA 7110.65V, section 4-8-1 (with my emphasis added in italics):
Approach clearances are issued based on known traffic. The receipt of an approach clearance does not relieve the pilot of his/her responsibility to comply with applicable Parts of [the] Federal Regulations and the notations on instrument approach charts which levy on the pilot the responsibility to comply with or act on an instruction; e.g., “Straight-in minima not authorized at night,” “Procedure not authorized when glideslope/ glidepath not used,” “Use of procedure limited to aircraft authorized to use airport,” or “Procedure not authorized at night.”
FAA directly advises pilots of our responsibility to adhere to these notations in Section 5 of the Aeronautical Information Manual (AIM):
Section 5. Pilot/Controller Roles and Responsibilities
5-5-4. Instrument Approach
a. Pilot.
- Be aware that the controller issues clearance for an approach based only on known traffic.
2. Follows the procedure as shown on the IAP, including all restrictive notations, such as:
a. Procedure not authorized at night;
b. Approach not authorized when local area altimeter not available;
c. Procedure not authorized when control tower not in operation;
d. Procedure not authorized when glide slope not used;
e. Straight-in minimums not authorized at night, etc.
f. Radar required; or
g. The circling minimums published on the instrument approach chart provide adequate obstruction clearance and pilots should not descend below the circling altitude until the aircraft is in a position to make final descent for landing. Sound judgment and knowledge of the pilot’s and the aircraft’s capabilities are the criteria for determining the exact maneuver in each instance since airport design and the aircraft position, altitude and airspeed must all be considered.
Air Traffic Controllers separate airplanes from other airplanes. They are not responsible for protecting pilots from themselves. It’s your responsibility to research and adhere to any restrictions on approaches and landings. It’s all part of the awesome Pilot-in-Command responsibility you accept when you exercise the amazing freedom of flight.
