OK - below, we have the Air Chart segment showing the area of Lidle's flight - I've picked out in red the pertinent stuff; the narrow VFR corridor (the narrow solid blue line inside the red box), and its Northern dead end. The entire width of the gap between the two sections of skyline - buildings - flanking the river is around 2000 feet, less than half a mile.
While some sort of equipment failure still cannot be ruled out as contributory, looking at this leads me to suspect pilot error even more strongly as a major factor. According to FAA reports, the plane was flying Northward along the corridor at around 700 feet, then, at or very near the "Dead End", performed a sharp retrace ("U-Turn") maneuver during which the plane descended below radar - "dropping off the scope". Since the building was struck about 350 feet above street level, it is reasonable to conclude the plane continued to loose altitude as it performed its retrace maneuver. Now, folks used to viewing the world through a ground-bound vehicle's windshield may have difficulty with this concept, but in an airplane, what you see out the windows is governed by the plane's attitude. In a steeply banked turn, it is not only conceivable but highly likely the plane's occupants could not see the building as they closed on it; the cabin's roof would have been in the way.
Also, it is not at all uncommon - in fact it is notably characteristic - for a rookie pilot performing a sharp turn to loose altitude through the maneuver. While eyewitness reports from uninformed individuals indeed are unreliable, when multiple reports consistently highlight something in the same manner - in this case engine sound and the plane's apparent control difficulties, it is reasonable to conclude something is behind the similarities.
I now think what happened is that the plane attempted a "U-Turn" at the end of the corridor, its occupants lost sight of the obstructions toward wich they were traveling, at something in the vicinity of 110MPH (per radar track info before contact was lost) - a few hundred feet goes by real quick at around 100MPH; a second equates to just short of 1500 feet of travel. By the time they realized, if ever they realized, they were lined up on the building, it was too late by far to do anything about it, whether or not everything about the plane otherwise was functioning normally.
I'm still puzzled about a few things - one thing that just doesn't seem to make sense to me is why Stanger would have gone along with the idea of entering that corridor in the first place. Apparently, it was not a flight track with which Stanger was familiar - one very credible source indicates Stanger's flight log shows only one entry, a few years back, for that corridor, so apparently it was a route with which he was not particularly familiar. The route in well known to local pilots as not one to be attempted without considerable experience; I'm not familiar with it myself, but from what I've gathered, its a route avoided by most private pilots, an often crowded route flown mostly by well experienced commercial sightseeing and local transportation pilots.
Short version: with or without equipment failure, it appears to me at this point that pilot error was a major, perhaps primary, factor. Did the plane attempt too sharp a turn, bringing on a stall? Very, very possibly, and if so, opportunity for correcting things would have been even more severely limited, as the plane would not have been fully under control - a very, very bad thing to have happen when there isn't much air between plane and terrain.
