33° flaps T/O and steep approach mods on the BAe-146-300
I'm trying to find out as much as I can about these two mods for a BAe-146-300, ideally without having to pay BAeS for the information!
Does anybody have any experience of it? In particularly what I'd quite like to know is what they do to LDR and TODR, and whether either create any difficult handling or systems peculiarities? [If anybody knows what it cost your company to procure and fit it, I'll very happily buy you several beers for that information at the next convenient bash.]
G, memory fades, but subject to that; … Flap 33 takeoff was initially a RJ100 modification requested by CrossAir for use at LCY. They wished to retain their full silver service galley load! Subsequently the mod was offered for general issue, and I thought it could be applied to all 146/RJ variants, I have no knowledge of this other than for the RJ100. Check the ex Air UK 146-300s? I don’t know how much a retrofit costs; it basically changes the takeoff config warning logic, and ensures the integrity of the landing config warnings. There is a switch/annunciator which (automatically?) resets after takeoff. I don’t have the performance figures, but the aim was to ensure that the max RJ85 performance was achievable by the RJ100 on the original LCY 1100m runway (also with the same/acceptable noise footprint) for the same pax load. IIRC the RJ100 was slightly better getting off the runway but fairly obviously not in the climb.
The steep approach mod was a ‘standard’ retrofit/option which applied to all aircraft variants. The flight deck switch annunciator adjusted the EGPWS warning logic (available within the EGPWS) – basically doubling the approach slope capability. The selection resets automatically after landing. Either with this mod, or as a separate package, there was a performance benefit applied by AFM amendment (it was ridiculously expensive - cost recovery objective). The LDR was adjusted by the geometric effects of a steep approach, the use of a 35 ft screen for landing, and a further benefit based on actual landing data. Because all of the standard RJ landing data was flight tested from a steep approach, the shortened flare path distance was claimed for steep approach operations. The overall benefit varies with aircraft series.
I don’t recall any handling issues. Steep approaches require the aircraft to be fully configured before the precision approach (ILS/PAPI). The max glideslope varies with aircraft type, 5 kt tail wind limit, no tailwind for the -300/RJ100 and 5.5 deg max; which are very sensible for such operations. Autoflight systems were either self-adapting or used the switch input. Cat 1 limits were retained. But some authorities (illogically) increased the vis requirement – the over nose view improves with descent angle. 3 eng approaches / GA were authorised, but obviously not for takeoff.
Yes, even with poor memory, 5.5 for the larger aircraft. However, local interpretations were made. The specific certification requirement was for a precision steep approach applied to a straight-in landing and flare onto a runway. Some airfield approaches might enable a two stage flare from an offset steep approach or flight path adjustment before landing. I don’t recall Sion, but Lugano at 4.5 deg was flyable without any mods due to its non-precision ‘airfield’ approach path, and similarly at Aspen.
Safetypee in particular, that's brilliant - you I definitely owe a (real!) beer to
So in a nutshell, the LDR is reduced by the difference between 50ft/3° and 35ft/5.5°, which is always going to be 180m, near as dammit - since so far as I can tell there's going to be no change to braking effectiveness.
For the 33° flaps T/O, presumably the increased flap setting reduces Vs slightly and thus Vr and V2, giving a slightly shorter TORR and slightly steeper initial climbout segment? Does anybody have any numbers for the effects of this that I might be able to play with?
G, the LDR benefit is slightly more than pure geometry due to the use of real steep approach test data in the landing flare segment, and thus there is a further reduction. The takeoff theory is as you surmise, but from memory the differences were in the thickness of the line, for the same load, but obviously at a higher weight for the RJ100. Therefore perhaps the flap 33 improvement could be quantified by the differences in aircraft ZF weights RJ85 vs RJ100.
Hoppy, that’s interesting; do the values you quote originate from the flight manual? IIRC the 146 certification (AFM) was pre JAR (pre EASA). The steep approach criterion was a special condition (UKCAA version of a Canadian STOL document) and the 146 certification was read across to the RJ. I don’t recall any ‘EASA’ AFM; thus wonder if someone has either rewritten the books, or are the values based on EASA approved operational interpretations (EU-OPS)?