Probable Cause #9: Personal Minimums

Pilots flying under the rules of FAR Part 91 are allowed to attempt an instrument approach even when the weather is below minimums. But when skills are rusty, it may be time to be more conservative, as we see in this week's Probable Cause report.

This article originally appeared in IFR Refresher, January 2005.

When should the pilot-in-command of a flight decide that he is not going to fly a particular approach, or perhaps a particular flight, due to marginal or below-minimums weather?We all know that under Part 91 we can fly an approach even when the weather is reported to be below legal minimums, but is that ever the safe thing to do?In theory, there is nothing wrong with taking a look. If the airplane is flown along an instrument approach course down to the published minimums and the airport or runway environment isn’t in sight, you would follow the missed approach procedures for that approach and there should be no risk to the safety of the flight.But the reality is that too many airplanes begin approaches in weather that’s near or below minimums and wind up colliding with the ground or some other obstacle. These accidents are fatal most of the time. So should you bother with an approach when you know the chances of it being successful are minimal?The FAR 91 rules give us much more flexibility than our commercial brethren, who are restricted by FAR 135 or 121 from shooting a below-minimums approach if they are still outside the final approach fix or the minimum glideslope intercept altitude. So for the Part 91 operator, the issue of whether to fly an approach is left to the PIC. Therefore, each pilot must give the issue some thought before taking off into a situation that could require an approach below minimums.

The Look-See Trap

There is no record of what kind of weather briefing the pilot of a pressurized Piper Navajo received before departing LaGrange, Ga., in March 2002 for a night IFR flight to Darlington Field (KAID) in Anderson, Ind. However, there is a transcript of a conversation that the pilot had with an Indianapolis Center controller that indicates the pilot was well aware of the weather conditions at his destination. The excerpt picks up as the pilot is over Louisville, Ky. [Editor’s note: The conversations have been edited for readability. The content is unchanged.]

N125TT: Indy, Navajo 125TT, request.Indianapolis Center (IND ATRCC): 1TT [sic], say again.N125TT: Yeah, we just got the weather there for Indianapolis. It doesn’t look too good for approaches. What’s Anderson doing? Can you get the weather for me?IND ATRCC: Let me see what I can find. Stand by.

About 20 seconds later, the controller advised the pilot that the Anderson weather observation he had showed 300 overcast and one-mile visibility.

N125TT: Any better weather any place else? You guys are half a mile and 100 feet. That isn’t going to work. IND ATRCC: N5TT, Louisville is visibility five miles with light rain, broken 6,500, overcast 8,500. N5TT: I suppose we could make a try at Anderson and see what happens and then come back to Louisville, I guess. I got plenty of fuel.

But that didn’t end the weather discussion. The controller told the pilot that the inclement weather extended as far south as Bloomington, Ind., which was reporting a quarter mile in fog. The pilot then asked if it looked like it was getting worse and expressed his thoughts that perhaps he should head for Louisville rather than attempt the approach into Anderson. The controller told the pilot to stand by while he called Indy Approach for an update.The Approach controller told the Center controller that he had an airplane on the approach into Indianapolis Metro, a general aviation airport east of Indianapolis, and that they could see how he made out. They also discussed a report that Muncie weather (northeast of Indianapolis) showed a visibility of three-quarter miles.After the Center controller had given the pilot the update on the Indianapolis weather, the Approach controller called his counterpart back to tell him that the airplane on approach into Indy Metro had gone missed. The controller passed that information along to the pilot.We can surmise at this point that the pilot was busy weighing his options, because he had picked up a report that showed that Muncie’s weather had improved slightly to a mile and half visibility. During the next four minutes or so, the pilot and controller discussed the overall weather trend and whether or not it was improving. However, the pilot must still have had some trepidation, hinted at by his request for the controller to put him on the localizer to KAID at least five miles from the outer marker.In the course of the next 15 minutes, the pilot was handed off to Indianapolis Approach, which put him on a 360-degree heading to join the localizer five miles from the marker before handing him off to another controller at Indy Center for the approach.Meanwhile, instead of improving, the weather was deteriorating further. At 10:45 p.m., the Anderson AWOS reported a 100-foot ceiling with a mile visibility, winds from 190 degrees at six knots, a temperature of 6 C and a dew point of 5 C. This information was available to the pilot on the AWOS frequency.Even more revealing is the recorded conversation between the Center controller (CONT. 1), who would monitor the approach, and his relief (CONT. 2), who was being briefed on the weather and inbound traffic:

CONT. 1: The visibility and the weather is really crappy in the Muncie/Anderson complex. Had one guy go missed approach three times [at Muncie].CONT. 2: Wow.CONT. 1: And then he went up to Fort Wayne where the visibility’s about three miles better. You’ve got an inbound to Anderson right there. [The controller is referring to N125TT.] I expect for him to have a little bit of trouble getting in there [unintelligible].

The NTSB report does not indicate if the Navajo pilot was ever made aware of the other pilot’s attempts into Muncie.

Giving It A Try

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Anderson, Ind., (KAID) ILS Runway 30 Approach Chart (Click for larger version)

The ILS approach at Anderson that evening was to Runway 30. The inbound course was 298 degrees and the approach required that the aircraft maintain 2,700 feet until intercepting the glideslope just outside of the VIDEO outer marker/intersection. The decision height was 1,162 feet, 250 feet above the surface.The Indy Center controller told the pilot to maintain his heading of 360 degrees and intercept the localizer while descending to 3,000 feet. The pilot acknowledged the clearance.At 11:00 p.m. the controller cleared the pilot for the approach and told him to maintain 3,000 feet until he was established on the approach. The pilot said he was established at that time and the controller told him he was two miles from VIDEO, at which point the controller cleared him to leave the frequency.The pilot’s acknowledgement was the last transmission from the aircraft. The aircraft crashed 3.7 miles from the airport and well to the right of the localizer on a 105-degree heading from the field.Radar plots of the aircraft’s flight shows that the pilot intercepted the localizer on the 360-degree heading and flew it inbound. However, before reaching VIDEO, the airplane started drifting off the course to the right.The last plot before radar contact was lost due to terrain shows the aircraft at 2,800 feet just beyond full deflection of the localizer needle. The crash site was approximately halfway between VIDEO and the airport and about a mile to the right of the localizer. The pilot and his sole passenger were killed in the crash.The aircraft was thoroughly examined by NTSB investigators and no defects were found.The 52-year-old pilot had 1,011 total hours in flight with 927 as pilot-in-command. He had 680 hours of multi-engine time and 193 actual instrument hours. His logbook revealed that he was current for instrument flight. We don’t know much time or what type of training the pilot had in the P-Navajo that he was flying. A forensics and toxicology report was negative.We can only assume that the pilot listened to the Anderson AWOS and heard that the weather was deteriorating, because he knew that the weather in the area was not very good and in many places was at or below minimums.The NTSB blamed the accident on the pilot’s failure to maintain control of the airplane during the instrument approach.Also, they cited the low overcast ceiling and the pilot’s decision to attempt an approach into an airport where the weather was below minimums as contributing factors.

Decisions, Decisions

In making the decision to try the approach into Anderson, the pilot knew he had Louisville as a good alternate. So, his choice to make the approach is not necessarily a bad one. I have made the same decision many times in the past. Sometimes the approaches worked out and on other occasions they did not. However, looking at the radar plot of the aircraft’s track on the localizer, there may have been other considerations for this pilot.The radar plot shows that the airplane was descending as it flew northbound to intercept the localizer. The pilot flew slightly through the localizer during the intercept but corrected back to it and was on the centerline well outside of VIDEO at 3,300 feet. At that point the airplane started to drift to the right of the localizer as it continued to descend. The last radar plot shows the plane high at 2,800 feet when it should have been at 2,700 feet to intercept the glideslope. The track shows it continuing to track to the right of the localizer. In fact, at the last radar plot it was beyond full needle deflection.We don’t know what happened to the plane’s path below 2,800 feet, when radar contact was lost. Did the pilot correct back to the localizer only to wind up far to the right again? Or was he making a series of corrections back and forth along the localizer right before the accident occurred? And because he crashed well short of the runway, he must have had a full deflection of the glideslope needle, as well.In other approach accidents that we’ve studied, we have seen both occurrences. For example, a pilot who was not proficient might join the localizer and then fly back and forth trying to keep himself on course. He becomes so engrossed in this task that he neglects the glideslope needle though the aircraft is descending. Once full deflection of the glideslope is reached in either direction, the pilot has no idea how far off the glide path he is.We also have seen pilots who were not familiar with the aircraft they were flying have problems scanning an unfamiliar instrument panel. In this particular case, we don’t know how familiar the pilot was with this P-Navajo.Regrettably, we will never know what factors influenced the pilot’s decision to attempt the approach or what really happened the night the accident occurred.

Personal Minimums

So, how would you go about making a decision based on what the P-Navajo pilot was faced with regarding the weather?What you decide should depend on the personal limitations that you have developed for yourself. For example, if you have decided that your approach limitations are a ceiling of 500 feet and a visibility of two miles, then you should not be tempted to shoot the approach in the conditions that were present at Anderson.We don’t know if the pilot had any personal limitations, but this accident points out that there is a place for them. How else could you make a reasonable decision regarding any instrument approach if you don’t have a basis for doing so? The decision to “take a look” when the weather is known to be at or below minimums should only be made by pilots who are current, proficient and absolutely confident in their ability to safely fly the approach to minimums, then make another decision at the bottom of the approach as to whether a landing is in order or whether the missed approach should be flown.No thought should ever be given to descending below minimums on any approach. Though the pilot was considerably to the right of the localizer, this accident might have been prevented had he realized that he was at or below the decision height for the approach. I don’t believe he intentionally descended below that altitude, but instead he was having a hard time controlling the airplane in the conditions in which he found himself and he didn’t realize how low he was until it was too late. Again, we will never know.Many times the necessary decisions can be made on the ground before the flight begins. If the weather looks like it will be dicey on the other end, it might be better to wait it out. Or you can find an alternate that is forecasting conditions that will meet your personal minimums. Even if it unexpectedly deteriorates, there are still things you can do to complete the flight safely, albeit further from your destination than you probably want to be.First, make sure you have plenty of fuel. If that means making an extra stop along the way, so be it. You’ll be happy you have it if the weather doesn’t cooperate and you can’t land at your alternate.Pilots don’t like to make fuel stops because they take time. Airplanes are supposed to be time machines and in most cases they are. But when the weather is marginal, the time it takes to get to your destination is not as important as getting there safely.Knowledge is the key to completing any flight safely. You should keep yourself continuously updated on the weather while en route. If a trend is developing where airports in the area of your destination are reporting deteriorating conditions, start thinking about what it will mean to your flight. Play all the “what if” cards in your mind, and if you think it is necessary, turn around and go back to where you came from, or find an airport along the route where you can land and reassess your situation. That would be a good time to add more fuel.So, the decision-making is in your hands. Base them on your personal limitations and stick to them as if they’re written in the FARs. Then, if you find yourself confronted with the situation this P-Navajo pilot faced that night, your decisions will be very easy to make.

More accident analyses are available in AVweb’s Probable Cause Index. And for monthly articles about IFR flying including accident reports like this one, subscribe to AVweb’s sister publication, IFR Refresher.