Ive been having a few weird flights when it comes to the autopilot following the speed restrictions in the FMS. To the point that I have to take off the FMS setting, and put in the manual speed mcp dial and set it.

What part of 250/10000 does it not understand? I ve actually had this a couple times in the NGX too. This is on the climb and descent. I can understand a descent not meeting it if you have some weird profile, but this was standard and nothing special going on. There is no way it should be accelerating past 250 under FL100 if thats what I have set. ATC wasnt very happy to say the least even though I caught it only 10knots over. I had to knock it off FMS and restrict it via the MCP dial.

 

Anyone had this issue?

 

Or am i missing something here?

Could it be that the aircraft was very heavy on takeoff, and the minimum maneuvering speed (referred to as clean speed in the B747 type rating course) was higher than 250 knots? I do not actually own the MD-11, so I do not know whether the autopilot overrides the 250/10000 restriction in autoflight mode (or whatever the equivalent of VNAV is called). Even for a short flight (< 1.5 hours) with the B747 with a load factor of 80%, my clean speed with flaps up was 253 knots at 10000 ft.

I have it happen sometimes, seems to be an issue with the logic of it. If the vertical profile was not accurate at higher levels, it tends to drop the nose and accelerate.

 

Did you get any requests to add drag at any stage? What was your descent speed? I use 300 knots and it works better than 290.

 

 

Try this...

 

Type 250B/ into the scratchpad and press the LSK button to the right of the original 250/10000. Assuming no other issues and the FMC accepts it like the FMC in the NGX, the 250B/ should keep it at or below 250 until that waypoint. Since you have the NGX also check out the bottom of pg 35 of the Tutorial #1 for the NGX.

Ive been careful not to be at or even relativly close to maxiumum takeoff weight so there should be no issues keeping under 250. The md11 would have had a low speed protection as opposed to a high speed protection and that never came up. The vertical profile was as per the star. In the ngx there is specific waypoint restriction and there is a global restriction of 250/10000 so it should always keep to that unless there is some sort of wild circumstances in which case the autopilot would probably disconnect.

 

I will try 250B on next flights.

Even at weights in the low 500,000lbs area I've had the plane require a minimum clean climb speed of about 254 knots. The md-11 has a high wing loading due to using a slightly modified dc-10 wing, which is to small for the weight it carries. At max tow, I've seen minimum climb speeds of 289! Usually the flight crew will tell clearance delivery when filing their flight plan that they will require faster than 250 in the climb, so that atc can make space for them. Never heard of instances where the request has been turned down

When the weight necessitates a clean speed greater then 250 KIAS, it is not unusual to leave the flaps extended until above 10000 and then retract when the speed has increased above the minimum clean speed.

 

Craig

Really?

 

That does not seem like a very efficient idea, especially when it is perfectly acceptable to exceed the 250/10000 speed restriction (at least in the United States) if the clean speed is greater than 250 knots.

Just request high speed from ATC... you're too heavy to fly safely at 250 or below clean... you should be given the clearance... you could even do it before takeoff...

 

You can see the min clean speed on the MCDU...

 

A

One of the reasons for the 250 below 10 is that you can increase the volume of traffic in the terminal area because the traffic is limited to a speed. 10000 is a good alt because the aircraft will have travelled a reasonable distance from the airfield.

 

aentwis I can tell you now that saying you cant fly at 250 kts clean will not give you a clearance to disregard the restriction unless traffic permits.

 

Craig

Guys,

 

This 250 restriction under 10 thing needs to go. It is the most misunderstood, mis-quoted, and mis-applied reg out there, and I don't understand why. If you're going to try to follow real world regs, you need to go understand them before blaming automation for not "following" them.

 

Problem is...the automation is actually following them.

 

When you read the regs, make sure you actually read the full section. Regs are not like workflows where you stop as soon as your case meets the condition given. In this case, read parts (a through (d:

§ 91.117 Aircraft speed.

 

(a Unless otherwise authorized by the Administrator, no person may operate an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots (288 m.p.h.).

(b Unless otherwise authorized or required by ATC, no person may operate an aircraft at or below 2,500 feet above the surface within 4 nautical miles of the primary airport of a Class C or Class D airspace area at an indicated airspeed of more than 200 knots (230 mph.). This paragraph (b does not apply to any operations within a Class B airspace area. Such operations shall comply with paragraph (a) of this section.

(c No person may operate an aircraft in the airspace underlying a Class B airspace area designated for an airport or in a VFR corridor designated through such a Class B airspace area, at an indicated airspeed of more than 200 knots (230 mph).

(d If the minimum safe airspeed for any particular operation is greater than the maximum speed prescribed in this section, the aircraft may be operated at that minimum speed.

 

While most people simply quote 91.117(a, the important part of this discussion is (d. Note that if the minimum safe airspeed for any particular operation is greater than the max of 250, then the aircraft may be operated at that speed.

 

So, since the FMC finds that the aircraft is too heavy to meet that speed restriction in a clean state, it disregards that limit.

 

Conclusion:

Autopilot Correctly Ignores Speed Restrictions, in accordance with 91.117(d.

 

Further clarification:

ATC has no authority to remove the 250/10 restriction, at all. They tested the idea around HOU up through 2004, but didn't implement it. To that end, if your aircraft needs to go faster than 250 under 10,000, there is no need to report. ATC expects this action from certain aircraft, the MD-11 being one of them.

 

Further, further clarification (since I know someone will point out mil ops):

The reason they make requests of ATC for unrestricted climbs or speeds is so ATC can get it cleared through the next sectors around him or her. Most controlled fields will have initial altitudes that a fighter will reach in much less than a minute. Instead of forcing the pilot to stay low, they ask for unrestricted and get up and out, and likely skip several frequencies. As an example, at IAD, you'd talk to ASPER/TILLY, LURAY, and probably two center sectors (high and superhigh). After leaving tower, that's four frequencies to switch to just to get passed to the next because of the fighter's climb performance. Instead, IAD Tower notifies Potomac (ASPER/TILLY and LURAY) of the request, along with Washington Center. Both facilities say their requests of tower for coordination, but likely approve it. Tower clears, aircraft goes up and out, and switches right to the relevant center sector freq. None of that is regulatory in a direct sense. In the indirect sense, the regs require you to comply with ATC, and in normal operations, you'd only get cleared to each sector's max altitude (or as dictated by SOP), which slows the climb.

 

 

 

 

Again, if you're going to apply real world regs in making the argument something is behaving incorrectly, make sure you understand said regs. Otherwise, you're just perpetuating the same stupid simisms that gave you this misunderstanding in the first place.

Agreed, and watch some of the ITVV videos (747 and MD-11 in particular). Both are faster than 250 below 10000 ft, and it is handled smoothly by ATC and pilots alike.

 

The MD-11 flies fast. If you need slower, delay clean-up.

 

Best regards,

Robin.

I just explained why. By restricting traffic to a specified speed you can actually increase the number of aircraft that can be handled in a specified piece of airspace.

 

I don't know your background scandinavian13 but your post is crap

Actually, it is ultimately up to ATC. If they clear you faster, you can do it. You need to request it. If ATC deny it, you can't do it. This even applied to Concorde! 250 kts unless cleared faster (then she flew at 400 kts below 10000 ft after clearance!).

 

Best regards,

Robin.

Concorde was dealt with as a special aircraft essentially due to its fuel state.