B737 Next Generation Undifferentiated
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 100; Flight Crew Type 6000
ATC Issue All Types
General None Reported / Taken
Airport; Procedure
While holding short of Runway XXL on L at ZZZ; I was observing numerous aircraft landing on both runways. There was a Company aircraft holding short of Runway XXR on L; between the runways. Tower had cleared a small general aviation aircraft to land on Runway XXL. As that aircraft approached the threshold of XXL for landing; Tower then cleared the Company aircraft holding short of Runway XXR for takeoff (or maybe it was Line Up And Wait; I do not remember). The Company aircraft then increased power to move forward. Simultaneously; the small aircraft was now crossing the Runway XXL threshold behind the Company aircraft; at about 10 feet AGL; and the jetblast of the Company aircraft caused the small aircraft significant controllability issues; the aircraft appeared to be blown into very steep bank angles and was tossed around; I thought the aircraft was going to flip upside down due to the violence of the motion. The small aircraft appeared to be a high performance experimental type and went around; and I thought the pilot did an outstanding job of saving the aircraft from crashing.ATC should look at their procedures at Runway ZZZ for this scenario. Because large aircraft holding short between Runway XXR and Runway XXL have the back of their engines in close proximity to the Runway XXL threshold; there is a high risk of these jetblast situations causing problems for small aircraft landing on Runway XXL; especially since small aircraft tend to have much lower threshold crossing heights.  I recommend that Tower not clear a large aircraft to move from this position between the runways while a small aircraft is in proximity of the threshold while landing on Runway XXL. Alternatively; ATC could issue a warning on the radio to aircraft landing on Runway XXL to 'use caution for jetblast from moving aircraft' or something to that effect to warn the landing Pilot of the situation; which could then prompt the landing Pilot to adjust his flight path to cross the threshold at a higher altitude and be above any jetblast risk. I also recommend ATC review procedures and look at other airports in the US system where there is a frequent mix of large and small aircraft with runways in close proximity; similar to ZZZ.
B737 Captain reported seeing a light aircraft on short final to ZZZ airport suffer the effects of jet blast from a company aircraft moving into position on a parallel runway.