Stumbling over the Vref mentioned in the investigation update:
“… slightly below the maximum permitted landing weight when it landed in Kingston….”
“… at the Vref (landing) airspeed of 148 knots …”
Just doing the numbers now:
- - -assume GWt = 144,000 pounds (near Max Ldg Wt);
- -now grab a B738 perf manual, to find a Vref for that GWt:
Vref for Flaps 30 ~ 148 KIAS
Vref for Flaps 40 ~ 141 KIAS
April of 1976 had two cases of Rwy Excursion; both investigations focused on the approach quality; and those AARs include some early ideas on “stabilized” approach concept, and more information on “spool-up” of turbojet engine.
Flaps 30 vs F40 --
This stumbling over the FLAPS 30 approach (versus Flaps 40) was a consideration in the Rwy Excursion [off-end] of
AA625 /
27Apr76 B727-95, N1963; St Thomas, Virgin Islands. From NTSB AAR 77-1, pg 27 :
“… captain said that … he decided to use 30 degrees of flaps.
He stated that the aircraft at 30 flaps is more controllable, is easier to manage, and that, ‘you have a greater margin for what is ahead.’”
From AAR 77-1, pg 36+, “conclusions”
Finding #8: “… The use of 30 flaps instead of 40 flaps increased the landing roll, provided lower drag, lessened the decelerative capability of the aircraft, and made the aircraft more susceptible to atmospheric or aerodynamic factors which could produce a float.
Finding #11: The aircraft touched down about 2,500 to 3,000 ft beyond the runway threshold. Based on these distances, it could have been stopped within the confines of the remaining runway, but a safe go-around could not be made.”
From AAR 77-1, Appendix I and J include some 1970’s versions of what might now be termed the Stabilized
Approach “gates” [as later defined in FAA’s AC120-71, Appdx 2]. Notice that in 1976 that only “gate” was much LOWER (closer to the threshold) at about 200’ agl.
Today’s FAA’s “stabilized approach” gates were reiterated in the FAA’s LETTER dated 2/19/02
(FAA’s response to NTSB Recommendation A-01-69):“… Approach gates are points established by the operator as reference points for flightcrews to monitor the quality of their progress during an approach to a landing and to promote their situation awareness. Approach gates are points at which … limits are noted and stabilized approach criteria are checked. These criteria indicate whether an approach can continue or a missed approach should be executed….”
By FAA order, in IMC, pilots for any US operator now have that approach “gate” at 1000 feet above the threshold.
Especially when flying a TAILWIND approach, pilots fight the “energy management” element of the FAA’s “stabilized approach” concept; it must be mastered PRIOR to descending through that IMC 1000-ft “gate”: “… maintain the proper approach speed with the engines spooled up …”
[FAA Order 8900.1, CHG 0; 9/13/2007; VOLUME 4,
CHAPTER 2, Section 3, paragraph 4-221, “STABILIZED APPROACH CONCEPT”]
Flight Standards Information System (FSIMS)
? Does FAA Southwest Region understand this “energy management” element of their own “stabilized approach” concept? ??
Could any 140K Lbs B737-800 fly such a stable glideslope, with 14kts tailwind – and still keep the “engines spooled-up”????
You ask, “What is ‘spooled-up’ for that CFM-engine"?
FAA’s only answer to pilots is in their AC120-71A, Appendix 2, “... Power setting is … within the permissible power range for approach specified in the approved operating manual used by the pilot....”
FSF’s answer (same as Boeing’s) is in ALAR Briefing Note 4.2 –
“Energy Management”
http://www.flightsafety.org/alar_resources.html
click on: 4.2 — Energy Management [PDF 97K]
FSF, _Flight Safety Digest_, August-November 2000, pg 75-79 [five pages]
Table One: “Recommended Elements of a Stabilized Approach”, Item 6:“Power setting is ... not below the minimum power for approach as defined by the aircraft operating manual …”
If FAA authorized 15kt tailwind for the B737-800, then FAA and Boeing must show that pilots can still meet FAA’s “spooled-up” requirement, while flying a stable glideslope, with that greater tailwind, at that Max Ldg Wt.
[See this photo for Boeing's DRAG solution to attain "spooled-up":
http://i14.photobucket.com/albums/a341/nw969/B47.jpg ]
Hopefully, AA & their pilots association will offer FAA & Boeing a day or two to deliver the data, and users will get better ideas about CFM’s minimum “spooled-up” RPM. Users need better Data; the "regulator" must ensure that the manufacturer defines "engines spooled-up" (rather than put that obligation on the poor "operator" ):
Boeing and FAA should agree to
provide users with a
graph similar to that shown below; but now for this mishap- CFM-engine,
DISPLAY the scale of
N1-RPM along the vertical axis, and
define the
"spooled-up" N1 for this mishap:
Turbojet Acceleration CURVES picture by IGhhGI - Photobucket
