Recently we have seen a lot of codes used to unlock our products being offered for discounted prices. Almost all of them are bought using stolen credit cards. These codes will all be blocked by our systems and you will have to try to get your money back from the seller, we are unable to assist in these matters. Do be very careful when you see a deal that is almost too good to be true, it probably is too good to be true.

Jump to content
NorCali.Pilot

Aircraft stops climbing at FL280

Recommended Posts

Hello,

So I've noticed lately that while in a SPD Hold climb (166knots), at around FL280, the aircraft stops climbing in an effort to accelerate to Mach .74. This of course disables me from crusing anywhere higher than FL280. 

Any ideas of what I'm doing wrong? The throttles are in the Climb detent. 

Share this post


Link to post

166 knots is much too low an airspeed for climb in speed mode. Normally after takeoff, once gear, flaps and slats are retracted, you would accelerate to 240-250 knots until passing 10,000 feet, at which time you would accelerate to 290 knots.

 

At somewhere typically between 27,000 and 29,000 feet, the aircraft will reach the crossover point where 290 knots equals Mach 0.74, at which time the speed mode will switch to Mach.

 

The wing of a CRJ is designed to be most efficient at a certain speed and angle of attack. The aircraft does not have true autothrottles. When the throttles are in the CLB detent, the engines will produce a specific amount of thrust calculated to keep the N1 speed and EGT within limits. With a (basically) fixed amount of thrust, the selected speed is controlled solely by pitch.

 

If you select 166 knots for your climb speed, the nose is going to pitch up much higher than normal to keep the airspeed from exceeding that figure. That might give you a very high vertical speed at lower altitudes, but as the air becomes thinner at higher altitudes, the  efficiency of the wing will quickly drop, and you will find yourself farther and farther behind the power curve.

 

Perhaps “166” was a typo, and you meant “266” knots, but even that would be too slow at higher altitudes. I’d recommend targeting at least 290 knots as soon as you pass 10,000 feet, or even higher (say 300-310) knots if your final target cruise Mach number is higher than Mach 0.74.

  • Upvote 1

Share this post


Link to post
12 hours ago, JRBarrett said:

At somewhere typically between 27,000 and 29,000 feet, the aircraft will reach the crossover point where 290 knots equals Mach 0.74, at which time the speed mode will switch to Mach.

 

Is the AS CRJ actually switching automatically to M0.74? If so, that's odd. Our entire fleet has the switch-over at 31600ft pressure altitude, the same moment half bank comes on. There is no automatic switch-over between 290kts and M0.74, that's a manual action to regulate your climb profile if your company prescribes it or if it is deemed necessary. As far as I have seen, the same holds true for Cityjet planes, Air Nostrum planes, and the Lufthansa (Cityline/Regional) CRJs. Would surprise me if this is a customer option.

 

And even when the automatic switch-over occurs, it switches to the current Mach number at the time of the switch-over, not to some preset number. It shouldn't switch from say 250 KIAS or 310 KIAS to M0.74. That would trigger erratic flight behavior such as the aircraft pitching down to accelerate or up to decelerate. Creating the issue described (regardless of whether the 166kts is a very weird speed to fly). I haven't flown the AS CRJ in ages, but if this is (still) the behavior, then with all due respect it's not very accurate.

 

Share this post


Link to post

The switchover I am speaking of is of the displayed units associated with the magenta speed bug shown at the bottom of the PFD speed tape.

 

I'm not suggesting it will arbitrarily go to Mach .074 (specifically). Rather, that it changes its unit of measurement from IAS to Mach based on the climb profile selected in the FMS. If the pilot has selected a climb profile of 290/.74, the bug will change from IAS to Mach at whatever altitude in the climb that the current IAS equals the FMS selected Mach number, and that will normally occur before reaching FL 300.

 

This may very well be customer or system dependent. We operate two Challenger 850s (corporate CRJ-200), which have the latest Rev 4.2 FMS software, including (recently added) ADSB Out and LPV approach capability, and they both do this change automatically at the altitude where current IAS reaches the corresponding FMS climb profile Mach number.

 

The 700/900 fleet may be different. I am about to delve into the maintenance manual for the configuration strapping unit of the Proline 4 system on our aircraft to see if that option is selectable there. 

 

The pilot can. or course, switch the bug from IAS to Mach manually at any time by pressing the center of the AFCS Speed knob.

 

On these same aircraft, the half-bank mode indeed activates at a fixed altitude of 31,500 feet.

Share this post


Link to post

Alright, I misunderstood then. I seem to remember that the earlier versions of the AS CRJ I flew switches by itself, too early and to strange speeds. 

 

Still, all our aircraft have a default 290/.77 climb profile set in the VNAV pages but the magenta bug will not switch over from IAS to Mach until 31600ft. At this point, 290KIAS generally equates to M.79. This is a mix of FMS4.2 and earlier versions. Strange stuff. 

Share this post


Link to post

Our aircraft, being -200s with the smallest CF-34 engines of the CRJ series, tend to "run out of steam" in climb in any case - especially during the summer months when heavily loaded, and with ISA +10 (or worse) temps aloft. From what I have seen in jumpseat maintenance test flights, our pilots rarely use the autopilot IAS/Mach speed climb mode. They typically use V/S while monitoring climb rate and airspeed while approaching their cruise flight level, looking for a happy medium.

Share this post


Link to post

Thanks guys for the info. I'll try some more flights.    I want to operate the AS CRJ as close to the real thing as possible since I will fly flying the real thing pretty soon here. 

Share this post


Link to post
1 hour ago, NorCali.Pilot said:

since I will fly flying the real thing pretty soon here. 

 

With all due respect but if you think that flying 166 kts indicated in FL280 in an CRJ is in anyway realistic I would advise you to redo the whole aerodynamics part of your theoretical education and especially redo the high altitude aerodynamics part. 

 

And please also ask an experienced instructor about high altitude aerodynamics when you are doing the CRJ TR. 

 

Last of all read this report:

 

https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR0701.pdf

 

Good luck!

 

 

  • Upvote 1

Share this post


Link to post

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...