Aviation Safety Corner
this month's topic, I would like to continue our discussion on, "The Deadly Deluge." Research has shown
heavy rain can rob an aircraft of lift quickly and without much warning. This is Part II of IV.
Now, let's start our discussion with "Shear or Heavy Rain?" The following two case studies were first exam- ined in an article published in the Journal of Aircraft by Luers and Haines. Their rigorous studies suggested that heavy rain contributed more to the loss of performance than did the wind shear, which was blamed for the incidents.
Eastern Air Lines Flight 66, Boeing 727, John F. Kennedy International Airport, June 24, 1975: This accident could be considered one of the watershed events that spurred the entire effort in wind shear, but may be that wind shear was not the sole culprit in this case. The airplane crashed into the approach lights for JFK's Runway 22L during an ILS approach to the runway through a very strong thunderstorm that was located along the localizer course.
The NTSB determined that the probable cause of this accident was *the aircraft's encounter with ad- verse winds associated with a very strong thunder- storm located astride the ILS localizer course, which resulted in a high descent rate into the nonfrangible approach light towers.* The Board noted the flight crew's delayed recognition and correction of their reliance on visual cues, rather than their instruments, but added, "However, the adverse winds might have been too severe for a successful approach and landing even had they relied upon and responded rapidly to the indications of the flight instruments.*
Witnesses near the middle marker for Runway 22L observed the aircraft at low altitude and in heavy rain. Five witnesses described the weather conditions when Eastern 66 passed overhead with statements such as "heavy rain was falling" and "there was lightning and thunder, and the wind was blowing hard from directions ranging from north through east." People driving on Rockaway Boulevard stated that a driving rainstorm was in progress when they saw the aircraft hit the approach light towers and skid to a stop on the Boulevard.
The cockpit voice recorder (CVR) indicates the windshield wipers were turned on at approximately 700 feet and placed on high speed when the aircraft descended to 500 feet. The CVR verified the presence of heavy precipitation.
While the final NTSB report attributed the mishap solely to wind shear, later research analysis calculated the effect on the aircraft's trajectory of the combined effects of wind shear and heavy rain. The report concluded that the wind shear profile could have been overestimated by a factor of two and that it is very plausible that heavy rain was a factor, which degraded the aircraft's performance.
The results of this report do not prove beyond a doubt that heavy rain was, indeed, a factor. However
the rigor of the method survived scientific scrutiny by peers and certainly deserves merit.
Now, in conclusion, remember that ALL PILOTS should be alert to the possibility of a significant increase in descent rate and decrease in airspeed when penetrating a heavy-rain cell.
Don't miss next month's, Aviation Safety Corner, when we'll continue discussing, *Shear or Heavy Rain?* This will be Part III of IV.
Larry G. Harmon
FAA AVIATION SAFETY COUNSELOR
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