The Downgrade
Your client is flying the RNAV (GPS) runway 14 approach into an airport with field elevation 1,040 feet. You briefed the LPV line: decision altitude 1,240, visibility one-half mile. The LNAV line is minimum descent altitude 1,540, visibility 1 mile. Reported weather: overcast at 900 feet, 2 miles, wind calm. At 10 miles from the final approach fix the annunciation drops from LPV to LNAV even though the receiver shows adequate satellites. The published missed approach is: climb to 3,000, then climbing right turn to 5,000 direct the ABC VOR and hold. The control tower is closed, the CTAF is quiet, and the approach lighting system is NOTAM'd out of service. You have a working VOR receiver and an ILS on the field.
1. What does the loss of LPV mean for this approach, and does the reported weather change your decision to continue?
Read the worked answer
Legally: the LPV line is gone. Without lateral/vertical guidance to the LPV standard you may not descend to the 1,240 decision altitude. The applicable minimums are the LNAV minimum descent altitude of 1,540 and 1 mile visibility. Any vertical guidance the receiver shows on a non-LPV line is advisory and does not change the minimum.
Why it dropped: find out before you get to the fix - loss of WAAS integrity, a NOTAM restricting LPV at this procedure, a temperature limit, or an approach that was never LPV-capable in these conditions. If the box is the problem, that suspicion applies to the missed approach too.
Does the weather change the decision? Counterintuitively, it argues for continuing - and this is the reasoning most pilots miss. The ceiling is 900 feet above the ground. The LPV decision altitude is only 200 feet above touchdown, so at 1,240 you would still be in cloud and would almost certainly go missed. The LNAV minimum descent altitude of 500 feet above touchdown puts you below the ceiling base, where you actually have a chance of acquiring the runway environment. The downgrade is not the threat here; the missed approach and the fuel behind it are.
Brief the change aloud, confirm the new minimums and the new missed-approach start point, and continue only if you are genuinely prepared to fly the LNAV profile.
2. At the minimum descent altitude your client calls the approach lights in sight but not the runway. What may you do, and what is the correct call?
Read the worked answer
You may not descend on the strength of that call - but the reason matters.
- Descent below a minimum descent altitude before the missed approach point requires both the required visual reference and, for a straight-in approach, the airplane in a position to land normally. The list of acceptable references includes the runway, threshold markings, threshold lights, the visual glideslope indicator, the touchdown zone, and the approach lighting system.
- The approach lights appear on that list, but here they are NOTAM'd out of service. You cannot use an inoperative lighting system as your reference - and it is worth being skeptical of what he is actually seeing: a closed tower, an unlit field, and 2 miles visibility produce a lot of misleading lights.
- Even if the lights were serviceable, the approach-light allowance lets you continue only to a defined height above touchdown to look for the runway environment; it is not a license to land.
The correct response: at the missed approach point with no runway environment in sight, fly the missed approach. Take the controls if the client freezes, announce "missed approach" and the reason, and start the published climb immediately - the airplane is at 500 feet above the ground with the ceiling base above you and no tower watching.
After the missed, tell him what you saw and what he should have called, on the ground, not in the go-around.
3. Halfway through the missed approach climb, the GPS fails. What do you do, and what do you tell ATC?
Read the worked answer
This is the failure the brief should already have covered, because the published missed approach is RNAV-defined and you have just lost the navigation source that defines it.
Fly first:
- Establish a positive climb attitude and hold the initial climb altitude from the missed approach - 3,000 - as your baseline, since you know it is a safe altitude on this segment.
- The turn point to the ABC VOR is defined by distance from an RNAV fix; without the receiver you do not know precisely where that is. Do not turn early on faith. Fly the last assigned heading or the runway heading, level at 3,000, and stabilize.
- You still have the VOR receiver. Identify ABC, set the course, and you have a usable navigation source to re-establish the published routing and holding pattern - but verify the minimum reception altitude and terrain clearance for the route you intend.
Then communicate:
- Tell ATC the navigator has failed, state your position, altitude, and intentions, and request vectors and an alternate approach - the ILS on the field is a good answer.
- If the situation is genuinely hazardous, declare. There is no prize for a cautious-sounding transmission.
Finally, note for the debrief: you launched an RNAV approach with a NOTAM'd outage at the field and a known annunciation downgrade. The alternate plan should have been briefed before the final approach fix, not after it.