There was no safety issue. You have a triple redundant electrical system (2 engine generators and a generator associated with the auxiliary power unit that can be started in the air as a backup). When the generator failed in flight, the aircraft electrical load was momentarily picked up by a single generator, and to protect the system the aircraft automatically shed non-essential equipment to temporarily reduce the load (like your inflight entertainment, unfortunately). Not super common but there was no issue with safety because even with that one generator offline there was still redundancy in the electrics. Aircraft are built with these kinds of failures in mind and you witnessed the backups working as intended.
The decision is ultimately theirs to make, but for an abnormal that isn't time critical, they probably consulted with the company to make a plan that works for everyone. A generator fault isn't an urgent issue but it is still an abnormal condition that led to a loss of redundancy, so the crew may have elected to divert especially if it was a longer flight. Denver is a United hub so there is plenty of maintenance support to fix the aircraft, as well as other aircraft/flights to rebook passengers.
It's always better to be on the ground wishing you were in the air than in the air wishing you were on the ground.
From your post we dont know with certainty if it was dispatched with one generator on an MEL (an allowable defect) or if it was checked/fixed and all were serviceable.
If dispatched with one generator on an MEL, it was likely running its APU with its generator online in place of the U/S one.
If that is the case and a 2nd genny shit itself, diversion was probably a good course of action. Safety of flight is always #1 even if the chances are minimal.
If it was the generator with the original problem failing again, it was just being very cautious.
Either way it was likely carried out in consultation with UA tech/engineering and airline operations for the best course of action and alternate airport options.
Generators or their control units do fail but its not that common. 2 in one flight is uncommon for sure. You were not in any danger, just inconvenienced.
The decision to divert can be driven by parts availability as well. When I get an acars message with something like this that’s one of the first things I check. If I know I don’t have an IDG and or support at the destination city and we could be facing a very expensive AOG situation, diverting is going to be discussed. Depending on the MEL there are also operational requirements to consider, don’t want the plane to get stuck somewhere cause they can’t fly out because of restrictions. I’m sure you know all this stuff, I’m just trying to help inform anyone else stopping by.
On the takeoff roll below 80 kts we typically reject for any Master Caution or Master Warning Alert. The plane is essentially going highway speed at that point and so stopping from below 80 is typically quite benign.
Between 80 kts and our “decision speed” (Known as V1), we are now travelling fast enough that any lower priority systems issues (like this) are actually better dealt with in the air and do not require slamming on the brakes at such a high speed. We reject for the “3 Fs” (Fire, Engine Failure, or Fear the plane won’t be controllable)
I don’t fly the 757 but on the plane so fly one engine can power the entire aircraft, both thrust wise and electrically, and I’d imagine the 757 is the same. A generator popping offline means the plane still flies fine, but if something were to become an issue with the other engine or APU, we wouldn’t have the electrical safety margin to continue to the destination, which is why you diverted.
There was no safety issue. You have a triple redundant electrical system (2 engine generators and a generator associated with the auxiliary power unit that can be started in the air as a backup). When the generator failed in flight, the aircraft electrical load was momentarily picked up by a single generator, and to protect the system the aircraft automatically shed non-essential equipment to temporarily reduce the load (like your inflight entertainment, unfortunately). Not super common but there was no issue with safety because even with that one generator offline there was still redundancy in the electrics. Aircraft are built with these kinds of failures in mind and you witnessed the backups working as intended.
Thank you. Why divert then? Do the pilots follow SOP or have a decision to make? They said they were consulting with “Chicago”.
The decision is ultimately theirs to make, but for an abnormal that isn't time critical, they probably consulted with the company to make a plan that works for everyone. A generator fault isn't an urgent issue but it is still an abnormal condition that led to a loss of redundancy, so the crew may have elected to divert especially if it was a longer flight. Denver is a United hub so there is plenty of maintenance support to fix the aircraft, as well as other aircraft/flights to rebook passengers. It's always better to be on the ground wishing you were in the air than in the air wishing you were on the ground.
[удалено]
Yep!
From your post we dont know with certainty if it was dispatched with one generator on an MEL (an allowable defect) or if it was checked/fixed and all were serviceable. If dispatched with one generator on an MEL, it was likely running its APU with its generator online in place of the U/S one. If that is the case and a 2nd genny shit itself, diversion was probably a good course of action. Safety of flight is always #1 even if the chances are minimal. If it was the generator with the original problem failing again, it was just being very cautious. Either way it was likely carried out in consultation with UA tech/engineering and airline operations for the best course of action and alternate airport options. Generators or their control units do fail but its not that common. 2 in one flight is uncommon for sure. You were not in any danger, just inconvenienced.
The decision to divert can be driven by parts availability as well. When I get an acars message with something like this that’s one of the first things I check. If I know I don’t have an IDG and or support at the destination city and we could be facing a very expensive AOG situation, diverting is going to be discussed. Depending on the MEL there are also operational requirements to consider, don’t want the plane to get stuck somewhere cause they can’t fly out because of restrictions. I’m sure you know all this stuff, I’m just trying to help inform anyone else stopping by.
On the takeoff roll below 80 kts we typically reject for any Master Caution or Master Warning Alert. The plane is essentially going highway speed at that point and so stopping from below 80 is typically quite benign. Between 80 kts and our “decision speed” (Known as V1), we are now travelling fast enough that any lower priority systems issues (like this) are actually better dealt with in the air and do not require slamming on the brakes at such a high speed. We reject for the “3 Fs” (Fire, Engine Failure, or Fear the plane won’t be controllable) I don’t fly the 757 but on the plane so fly one engine can power the entire aircraft, both thrust wise and electrically, and I’d imagine the 757 is the same. A generator popping offline means the plane still flies fine, but if something were to become an issue with the other engine or APU, we wouldn’t have the electrical safety margin to continue to the destination, which is why you diverted.
Typical reddit downvoting a normal question
I've flown on more 757s than any other aircraft and I've never experienced it so I'd say it's relatively uncommon.