747.200
348 tons TOW
Initial departure track relatively clear with SID calling for R turn which at that weight would happen around 3000 ft. Light rain / green showing on wx radar ahead. No previous reports of anything untoward.
Around 4500 ft, Flap 5 entered what I can only describe as a washing machine.
Extremely heavy rain and then numerous hail events, so much so that we had to yell at each other when calling trends.
Subsequent data analysis showed numerous IAS excursions, the most extreme being IAS fluctuation from 269 kts - 198 kts in 2 seconds (overspeed and under speed for wt/configuration)
Told by ATC to maintain 9000. Unable.
Told to maintain 11000. Already thru 11500.
Got call out "get everyone away from us and need unlimited climb"
FO flying, doing superb job just maintaining attitude / wings level and moderate climb power setting to attempt to dampen speed excursions.
Entered descending airmass. A/C rapid descent from approx 11500' to 7000' speed stable max cont thrust.
Ascending airmass 7000 to end of event.
Broke out of cell at 15000 ft
Cleaned up and then first FE then myself did inspection leading edge and cowls. Nil damage evident.
Continued.
Humbled.
I have 10 years on 757/767 (8 yrs on 747 variants) and, whilst I think the 5 and 6 are magnificent aircraft, I do not believe they would have handled this event as well as the old girl.
Speak to anyone who has flown the classic and they have a deep respect and connection with the aircraft, for obvious reasons.
Footnote: after my call to ATC for "some space" the wx ahead was passed to Kallita classic behind us. His response "No !!!!, we're in it !" brought a smirk amid a high workload event.