Pre-2002 B738 Flaps 40 Oddity
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Pre-2002 B738 Flaps 40 Oddity
Good day women and men of the skies - I had the unfortunate experience yesterday of flying a specific 737-800 (delivered in 2001) that as I later found out is infamous for large roll tendencies when approaching with Flaps 40. As I was looking through the document archives of company issued laptop I found an old message relating to this, basically saying that aircraft built up until mid-2002 exhibit 'asymmetrical flow separation' at the inboard flaps and the 'wing-body interface' - Boeing is supposedly aware of this and subsequently incorporated a modification from mid-2002 on but does not offer a retrofit due to 'unjustifiable cost'. Neither me nor the captain were aware of these problems with this aircraft before the flight, hence the captain made a couple of TLB entries post-flight - we experienced the following:
Two night approaches, both ILS, wind calm, no turbulence - both Flaps 40, large roll tendency to the right, required four units of aileron to the left to maintain wings level or alternatively 3 units of left rudder trim (in turn requiring 76 N1! to maintain speed) Buffeting was also encountered well above Vref40 as well as right wing drop during thrust reduction at flare. Felt more like an approach over open terrain in summer - but there surely weren't any thermals past midnight rocking the plane like that.
The chat with the bloke from maintenance after the flight wasn't all too helpful, he said that the pilots normally know not to use Flaps 40 on that specific airplane...
Nonetheless this seems very strange to me, if there is a known problem like that shouldn't there be a permanent note in the TLB or even a placard in the cockpit to warn crews of this behaviour?
Just wanting to know whether you have had similar experiences with old 738s...
Thanks a bunch, best regards
Stbyrud
Two night approaches, both ILS, wind calm, no turbulence - both Flaps 40, large roll tendency to the right, required four units of aileron to the left to maintain wings level or alternatively 3 units of left rudder trim (in turn requiring 76 N1! to maintain speed) Buffeting was also encountered well above Vref40 as well as right wing drop during thrust reduction at flare. Felt more like an approach over open terrain in summer - but there surely weren't any thermals past midnight rocking the plane like that.
The chat with the bloke from maintenance after the flight wasn't all too helpful, he said that the pilots normally know not to use Flaps 40 on that specific airplane...
Nonetheless this seems very strange to me, if there is a known problem like that shouldn't there be a permanent note in the TLB or even a placard in the cockpit to warn crews of this behaviour?
Just wanting to know whether you have had similar experiences with old 738s...
Thanks a bunch, best regards
Stbyrud
Last edited by STBYRUD; 14th Jul 2010 at 16:42.
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This issue is one of the reasons why several airlines do not recommend to use flaps 40 at all, only short RWY or CATIII flaps 40 landings are accepted.
With the quote above, what would stop the operator experiencing such an occurrence on an actual CATII/III approach, especially regard to automatic thrust reduction at 27'RA. The 'wing drop' would certainly induce a bit of rectal clenching!! And as for short runways - I always like to see the approach as stabilised as humanly possible!!
