FAA green line on CL-65.. in depth question

[Rez O. Lewshun]

Looking for a reference or documentation that the FAA green line (on US registered aircraft only) on the CRJ airspeed tape is only valid in the landing configuration. Flaps 45 and gear down.

The Canadair CRJ Pilot Reference Manual (PRM) says any flap/weight.

Also...what specific FAR dictates this?

Requesting reference/info...

 

[mynameisjim]

I have always thought that the green arc was the normal operating range, meaning any weight, flap, or gear setting. therefore the white arc is for the landing configuration. not sure about the CRJ, didn't know any transport category airplanes had a green line. i know part 25 dictates how the stall speed of a transport category airplane is measured, and i believe in there it is the takeoff condition stall speed, so takeoff flaps, gear up, CG bad, idle thrust, etc etc etc.

anyone else wanna give it a shot?

 

[Rogue5]

[font=MS Sans Serif,verdana,arial,helv][size=-1]With respect to the CRJ EFIS, the "Green Line" is a variable horizontal line indication that moves up or down along the speed tape depending on configuration and weight. This has nothing to due with white or green "arcs" seen on G.A. airspeed indicators.

Although intended for reference during approach and landing (and T/O), it often begins to climb uncomfortably close to climb speed at high altitudes on hot days at heavy weights. Bombardier has said to disregard this cue as it is calibrated for low speed dirty configurations, although many pilots are wary of climbing at speeds near or below the green line, or up to altitudes that bring the green line up when maintaing 500 fpm...

From Bombardier Service Letter RJ-SL-27-052:

RJ-SL-27-052

ATA: 2735

DATE: 09 MAY 02

SUBJECT: Green Line Test Procedures

MODEL: CL-600-2B19

APPLICABILITY: FAA Certification Standard Aircraft only

PURPOSE:
To provide a test procedure for the verification of the Low Speed Awareness Cue, also
referred to as the Green Line.

DISCUSSION:
The low speed awareness cue (Green Line) reference is an aid to the flight crew to
determine the maneuvering margin (approach speeds in relation to stall speeds) available
for any flap setting at any time during an approach or departure. The design of the low
speed awareness cue has been optimized for use during departure and approach.

Operators are experiencing low speed awareness cue differences between both PFD’s. It
should be noted that any lateral gusts might affect the reading on each PFD. Slight
differences in the airflow over the left and right AOA (Angle Of Attack) vane caused by
side-slip or turbulence at high airspeeds and/or altitudes may cause splits in the individual
green lines on each PFD. This is not an indication of a Stall Protection System
discrepancy.

[/size][/font]

 

[skyslug]

There is a reference to this, unfortunately I don't have access to it. I've seen the bulletin on this about 4 or 5 years ago after asking MX for some info on it. From my froggy memory I believe it states something to the effect that it's invalid at cruise, and perhaps some other phases of flight.

I know, that was absolutely NO help whatsoever but I know someone else out there knows more about this than I do and has documentation for you.

edit: and there it is! Thanks!

 

[mynameisjim]

The airbus has a feature thats calculated called 'green dot' which is the maneuvering speed flaps up. the computer that calculates it makes real time calculations up to 15,000 feet, then after that it becomes less reliable because its based on green dot at 15,000 plus a few knots per thousand feet. i wonder if it is the same with the CRJ green line at upper flight levels.

 

[SkyWestCRJPilot]

The following quote is from one of our instructors here at SkyWest:

"GREEN LINE- is displayed on the PFD airspeed scale as an indication of approximately 1.265 Vs for the Flap configuration. It can be considered as a bracket that extends from the top of the slow speed checkerboard to 1.265 of stall speed. It reacts in the same way as the shaker boundary and can be viewed as an extension of it (not approved by the FAA as a sole means to fly an approach).

• Green line is subject to certain errors, which must clearly be understood before we can properly interpret it:

 The position of green line is calculated according to information from the stall protection computer, which can only compute the pusher-firing angle for the present Mach number. This means that green line can never be more accurate than (+/-) 2 to 3 knots. Furthermore, the greater the difference between the present Mach number and the stalling Mach number, the more green line will be in error on the high side. The closer that we fly to Vref for the flap setting, the more accurate green line becomes.

 The stall computer and Green line have different settings for each flap configuration. During flap extension or retraction, green line is momentarily unusable. We cannot rely on green line if the flaps have failed in any position other than the approved flap settings.

• The margins that we recommend for maneuvering and final approach allow for the increase in stalling speed as bank and/or G increases. This can be seen as the green line climbs to some higher value. Remember that as long as you are at green line or above, you have sufficient margin for 30 degrees of bank. During turbulence at speeds close to Vref, green line movement is relative to the angle of attack and could be used as a further confirmation of gust margins during approach. It is safe to say that if you are below green line in stabilized 1-G flight, you are below Vref for the flap setting.

Simply said, the green line at FL350-cruise flt-m.74 is not accurate because the aircraft is futher away from the stalling mach number. Example: Next time your in the sim, have the insructor "slew" you to 35000 feet and "slew" speed to 262kt(m.77). The green line will appear at a speed of approximety 230kts indicated. Do you really think the stall speed is that high at this altitude. Of coures not. Now, with the auto-pilot on, reduce the thrust to flight-idle. Which direction will the green line move (up, down or stay the same)? It will slowly move down as airspeed decreases. However, as the explanation stated, the aircrafts mach speed is decreasing therefore the green line is becoming more accurate as the aircraft decelerates. As the the aircraft approaches approximately 200kts indicated, the green slows to almost a complete stop and airspeed of the aircraft falls below the green line. Up to this point, we have NEVER fallen below this reference indicator until now. Now guess what you're going to see? That's right the LOW SPEED CUE (red barber pole). Now you're close to the stall. Again, keep in mind this was done in a 1g maneuver. Now,at the same conditions as previously mentioned, kick the auto-pilot off and perform a 45 degree back turn, and watch the green rise to a higher value than where it originally started. This is because in a banked maneuver, the stall speed has now increased by virtue of increased load factor. In this example, the difference between the present MACH number and the STALLING MACH number was reduced by the increase in bank therefore making the green line MORE accurate.
Now, if you're flying around, 370, 390, 410, and in a 1g straight and level cruise flight (m.74), you may see the slow speed cue and the high speed cue within the range of the air speed indicator. We all know that this is known as "coffin corner". The very small operating area of flight. Even though we are at cruise m.74, this mach number is much closer to the stalling mach number than it was previously at FL350. Therefore, once again making the green line more accurate in this example."