Can any one explain the reason behind allowing any jet aircraft (not using an auto-throttle) to overspeed?
I wonder why there is no automatic function to restrict or prohibit engines from doing so.
I’m in the HondaJet at the moment; not paying good enough attention after reaching cruise alt, when I receive the Overspeed audible. Looking down I see it’s WAY, WAY overspeeding and I’m already near max. That’s terrifying! The next minute or so freaking out the HondaJet may rip apart before getting down to cruise speed.
So that’s how this topic question happened.
It’s such a tech-driven plane too. Why would they not build in a safety to prevent it?
Airbus has some overspeed prevention - but it only applies whenever the autopilot is managing speed:
The AP will remain engaged throughout most of the overspeed events encountered in cruise.
The AP will only automatically disconnect if there is a large or prolonged VMO/MMO exceedance.
However on aircraft certifying entirely new technologies which actively take control over critical systems takes much time and is cost intensive. The pilots are the ones responsible for passenger safety in the first place so they have to be able to overwrite whatever a system is doing.
That was something which lead to the MCAS related crashes as specific procedures were not trained and pilots did not know about what MCAS does in the first place.
Even if it seems to be a good idea to restrict aircraft completely from overspeeding one have to keep the failure case in mind (like if the aircraft got two different speed readings from blocked pitots) which adds complexity and cost.
So I think it would be possible to do something like that regularly but likely it’s too expensive for the rare cases an aircraft really overspeeds to a point damage will occur the red line should not be crossed but aircraft irl can stand higher speeds for some time.
The trouble is the more systems you add to an aircraft the more likely it is that those systems will fail and cause a catastrophic failure. Overspeed sensors could go wrong and refuse to allow the engine to power up when power is exactly what is required. Watching how much power we apply is no different to what we do in a car, its actually very easy to over rev and engine but we dont, we carefully control how much gas we give it, same with an aircraft.
Here’s an example. IRL, assuming the autothrottle is available, the Longitude will automatically engage the autothrottle, slow down, reset the original throttle positions, and disengage. In the event that you’re descending too aggressively and exceeding Vmo/Mmo, and the autothrottle is either already at idle or not available, the autopilot will shallow the descent angle and ride the appropriate limit speed. Similar functionality exists for stall prevention as well.
Well to chime in as well, here is what we learn in flight school. While power does provide thrust to gain speed, most of the time they will always teach you that pitch = airspeed and power = altitude. Granted I never flown the Honda Jet in the sim, I have read many reviews that it is a great aircraft. Only way you’re going to overspeed is if you have engines running at a pretty high-power setting and you are pitching down without noticing.
However, if the aircraft does have an auto throttle and AP to maintain cruise altitude, I do not see why the aircraft will all of a sudden overspeed in cruise. I am not calling out your skills or anything but if the AP is setup correctly with AT it should not overspeed at all. Other reason I can think of is a bug in the aircraft or sim. I am sure most technologically advanced aircraft have some system that will prevent the aircraft from over speeding most likely when the AP is engaged. If you are flying manually and the aircraft does not have a system like the airbus to prevent over speeding, most likely you will overspeed if you are not paying attention to what the aircraft is doing. After all, in most aircraft if you are flying manually, you are responsible for the way the aircraft is going to perform.
They no longer teach pitch = airspeed and power = altitude. Definitely not for jets.
Jets in the flight levels at close to Mach fly very close to overspeed. Now, granted the warning is far enough away from where damage will occur that it’s safe, but, jets at high altitude can very easily rip their wings off. Check out the U2’s flight regime at very high altitude. It was quite the dangerous plane to fly. I think the difference between stalling and ripping the wings off was on the order of 10’s of knots at very high altitude. There are others here on the board who can speak to these concepts more intelligently than I. Be that as it may, at 40,000 ft, the difference between cruise and overspeed is not that much.
As my flight instructor taught me, pitch for airspeed and power for altitude is about as useful as knowing how to walk on your hands. It’s possible, but ultimately just not practical. Generally speaking, if you’re flying point to point in something with a constant speed prop or a jet, you just don’t touch the throttles that much.
While the U2 is a special case of trying to fly subsonically at very high altitude, it’s by far the exception. In the civilian world, there’s requirements to demonstrate handling qualities at the max speed for flight characteristics (beyond max operating speed), and demonstrate the ability to recover at something near the structural dive speed (loosely defined in airspeed, but usually about 0.07 Mach more than Mmo. Accidentally exceeding Mmo/Vmo in most aircraft is a non-event.
You may be right for jets that when flying close to mach it really does not apply but concept is still there. If I pitch the nose attitude let’s say 40 degrees up or more, even as you are at full throttle you speed will no rise much even at the FL and most likely bleed off, hence pitch = airspeed. It is a basic concept that they still teach all students, that is what I was taught as I was going through my PPL training 3 years ago.
My point is that with an AP and AT system onboard if it has one because like I said I have never flown the HondaJet but I am certain it does, most automated systems do such a good job at keeping an aircraft out of those zones, that is why I say the aircraft should not be over speeding at all unless there is a huge gust of wind that throws it off and such. Most aircraft with those advanced systems rarely ever overspeed which left me to suggest that either he encountered bugs or was not set up properly with the AP. I would assume he would have an AP engaged at cruise.
I can tell you I’ve been on a lot of Jet Blue flights in A320 and A220’s, pretty much all at 38,500 ft; note that’s above the Recommended Max Altitude.
That is not the point we are trying to get at, I know the flight envelope at cruise is small at high altitudes, it can also be called “Coffin Corner”. What the OP poster was asking is how come there is not a system in place to prevent the aircraft from overspeeding. What I mentioned is most aircraft are pretty capable of maintaining an appropriate airspeed to keep the aircraft from overspeeding when an AP is engaged alonside with a AT. As long as those are engaged it tries to keep the aircraft from overspeeding. Some manufacturers just don’t deem it necessary to have one as that is what a pilot is trained to do when flying manually, to ensure everything runs smoothly and within limits. Plus, to be honest I don’t think you will ever see any pilots not using an AP and AT passing 10,000ft again eliminating the need for an overspeed and stall protection as the automation is more than capable of avoiding those situations so long that it has been programmed correctly into the FMS.
Like I also mentioned for me I was not berating the OP skills at all because for all I could know, they could be a real-world pilot with more experience than me with these systems or maybe they might be completely new who is eagerly learning to fly. Hence why I said, “not calling out your skills or anything”. Add to the fact that I do not know the Hondajet systems, I also said “if” the aircraft has an AP and AT, it should rarely overspeed with automation set up properly.
IIRC there has been crashes due to wrong airspeed readings, causing A/T to slow the plane to stall.
So you can see why planes are allowed to overspeed.
Not ever overspeed warning is legit.
You can allow the car to overspeed too when keeping the pedal floored. Why should there be a limiter implemented - the car does not know if it´s in a 30km/h zone or on a freeway that is going straight until the horizon
A rev limiter to prevent the engine from exploding is good enough…
A jet also does not know if it´s in descent and getting too fast. And a jet must be overpowered otherwise it would not be able to climb with full tanks - so when pulling the thrust levers full forward to TOGA while being in a leveled flight it will of course overspeed after some time…
There is an autopilot auto-thrust in every* jet (except the CRJ) so overspeeding normally does not happen anyway.
Even more important than a heavy takeoff is an engine failure. All airliners are certified to lose an engine at V1, and must be able to complete the takeoff and climbout to clear any obstacles with only 50% power available (so 1 engine operating on a 2 engine jet; or 2 engines operating on a 4 engine jet.)
Thus, on any takeoff where you don’t lose an engine, you’re already 50% over-powered ;).
So, yes, jets will always be capable of overspeeding in level flight. Systems do exist to prevent this (autothrottles and autopilot) but they can be turned off, for good reasons already discussed. There are differing design philosophies in the industry regarding when and how much control should reside with the pilots vs the automation, but almost every airplane can be taken down to fully manual control (inputs may still need to go through a computer, but it’s not applying any of its own logic anymore.)
And it is still important for airline pilots to remain proficient at hand flying. Sometimes it seems that simmers think airline pilots hardly fly at all. I routinely hand fly 737s up into the 20s, and typically click the automation off on base on a nice day. You can bet that if you do this for a career, a day will eventually come when you’ll need to actually fly the airplane… and on that day, it’s a good thing if handflying is second nature to you vs an abnormal situation all on its own.
Please note that the REC MAX ALT in the graph is just an example for that particular weight. If Jet Blue are flying an A320 at 38500 (a very strange cruising altitude by the way, it would normally be 38000 or 39000 or 37000, not 38500) then you can be sure that the REC MAX was higher than that for that particular flight.
To the OP, some jets do have overspeed protection, the A320 will pitch up to prevent overspeed even in manual flight, but ultimately you’re the pilot, it’s your job to fly the plane.
On the topic of max speed vs cruise speed at altitude, I’ve already uploaded this photo to the forum for another thread but it’s also a good example of the small operational speed window at high altitude. About 13 knots to Vmo and 20 knots to Vls.
The next minute or so freaking out the HondaJet may rip apart before getting down to cruise speed.
the red line should not be crossed but aircraft irl can stand higher speeds for some time.
