Weather ‘suddenly and severely deteriorated’ during Oshkosh departure

This is an excerpt from a report made to the Aviation Safety Reporting System. The narrative is written by the pilot, rather than FAA or NTSB officials. To maintain anonymity, many details, such as aircraft model or airport, are often scrubbed from the reports.

The pilot flying was a private pilot, without an instrument rating, in the left seat. I was providing some instruction from the right seat, but was mostly there to provide backup to a relatively new pilot on her first big cross-country trip.

The Pilot Flying (PF) had approximately 30 hours in type, and was becoming comfortable with the complexity of this high-performance single and the speed at which things happen. By prior agreement, I was serving as PIC on all flights.

On this flight from OSH to ZZZ, the planned training topics included: The OSH VFR departure procedure, managing the very busy traffic environment around OSH, en route simulated attitude instrument flying, and practice IFR approach.

We were departing OSH during EAA AirVenture, shortly after the airport opened in the morning. It was busy, but by no means crazy. We had reserved an IFR departure slot, but opted not to confirm it the day before, as the forecast was CAVU. We wanted to leave the scarce IFR slot for someone who truly needed it, and I wanted to give the PF the opportunity to perform the Oshkosh VFR departure.

We received a full ForeFlight briefing that morning, which showed CAVU at OSH and for the entire route of flight. From the ground at OSH, there wasn’t a cloud to be seen.

We were assigned Runway 27, which (per the Oshkosh NOTAM) required that we fly a heading of 270-360 at or below 1,300 feet MSL (500 feet AGL) until clear of the Class D.

As our route of flight was southeast, we planned to depart Runway 27 to the northwest, fly around the north side of the Class D, then proceed southeast on course.

All went as planned until we reached approximately 1-2 nm west of the departure end of Runway 27. We were climbing through 1,100 feet to 1,300 feet MSL, and the weather had suddenly and severely deteriorated.

I estimate that visibility was perhaps 3 sm, and as we continued our climb, we began to enter the ragged underside of an overcast layer that I estimate was around 400 foot AGL (1,200 foot MSL).

I instructed the PF to stop the climb, descend as necessary to remain below the cloud layer, and fly a heading of 360.

She leveled off at 1,150 feet MSL. Knowing that this was only 300-350 feet AGL, we were both on extremely high alert for towers, aided by the VFR sectional. I could see Lake Butte des Morts approximately 2 nm north, which (a) would relieve us from worrying about towers, and (b) had a sky that looked much brighter.

Once over Lake Butte des Morts, we could clearly see Lake Winnebago to the east, to which we proceeded at 1,200 feet MSL. Once over Lake Winnebago, weather improved very rapidly, and the rest of the flight was uneventful.

We were still listening to the OSH tower as we reached Lake Winnebago, and they continued to dispatch pilots to the northwest from Runway 27. Now that I had a small amount of mental capacity to spare, I called tower and informed them that conditions northwest of the field were “just barely VFR” and to exercise extreme caution.

They sent one more aircraft in that direction, who reported that conditions were “definitely not VFR.” That pilot returned to land at OSH, which was then closed to VFR departures.

In hindsight, I made several errors in judgment that morning:

1. The subsequent pilot was quite right: The weather conditions were definitely not VFR. When I made that report to the tower, I was fixated on visibility (which was, I believe, barely VFR — perhaps 3 sm). But when I had time to think more clearly, it was obvious that we were only just clear of cloud, not 500 feet below. Furthermore, even if clear-of-cloud had been legal (which it was not), 1,150-1,200 MSL was a very dangerous altitude. In this area, it was true scud running. We passed less than 1 nm from a tower less than 100 feet below us (although we had it in sight).

2. The moment that we encountered weather that was worse than forecast, we should’ve done as the later pilot did: Inform the tower that conditions were not VFR, and coordinate an eastbound turn (not withstanding the requirements in the NOTAM). In hindsight, I gave far too much deference to the procedure in the NOTAM, and did not want to deviate from its mandate. I didn’t want to be “the guy who screwed up the OSH departure and snarled traffic for everyone” — or worse, create a collision risk by being where I shouldn’t be. Yet it’s obvious that the extremely professional controllers would’ve managed the situation, and it would’ve been far preferable to scud running. I failed to exercise my ultimate authority as PIC (Pilot In Command) that morning, and in my opinion this was the most critical error.

3. In hindsight, the one clue that we missed was a METAR at PCZ, 29 nm northwest of OSH, showing OVC005. This should’ve told us that, although weather at and east of OSH was extremely VFR, it was much worse only a short distance away. At the very least, this could’ve prepared us for the possibility that we would encounter poor weather nearby, and have a complete plan ready. Had we been able to perform a standard downwind departure to the east, as we would any other time, it’s highly likely that we would’ve remained CAVU the entire time.

Primary Problem: Weather

ACN: 1838504