B737 Crashes on landing in South Korea

[StressMerchant]

-at no point does human/animal crew/passenger safety come into your consideration....?

Simple facts:
- The aircraft did not crash because the recorders became inoperative
- Failure of the recorders do not affect Continued Safe Flight and Landing (CSF&L)
- The recorders are not essential systems. In a complete electrical generation failure, only essential systems should be allowed to access the existing stored power.
- Both Boeing and AIrbus permit despatch with recorders inoperative, see your MEL. Usually allowable for a limited number of flights.

[Aquila]

-at no point does human/animal crew/passenger safety come into your consideration....?

Simple facts:
- The aircraft did not crash because the recorders became inoperative
- Failure of the recorders do not affect Continued Safe Flight and Landing (CSF&L)
- The recorders are not essential systems. In a complete electrical generation failure, only essential systems should be allowed to access the existing stored power.
- Both Boeing and AIrbus permit despatch with recorders inoperative, see your MEL. Usually allowable for a limited number of flights.

Yep, it seems like the may be inop for 8 flights or 3 consecutive calendar days on the bus...

[Patrick AL]

-at no point does human/animal crew/passenger safety come into your consideration....?

As noted:
1) CVR and FDR do not in any way affect the safety of the flight. They only assist with accident investigations (which can potentially affect safety of future flights).

2) All important causal factors are likely to be logged by the time the second AC bus shuts down. If you know what triggered the bus shut-downs, then you know the likely cause. There is unlikely to be any information to record after that point which is relevant to airframe safety.

...maybe for the specific incident it would serve no assistance, but certainly for all current and future type operations!

There is just no justifying a very basic oversight like this

-maybe the PICs should just carry one of these ----with Duracells!

[dollar]

Yet Airbus decided differently?

Yes - and I would say that in that regard, the Boeing is actually safer.

Airbus is 100% reliant on power. If you don't have at least one functioning hydraulic system, and a little electricity, you are already dead. As a consequence, they are forced to have multiple levels of power redundancy. 2x engines, 1x APU, 1x RAT and 2x batteries. Which means you have a lot of options for backup power to non-safety critical systems.

On the other hand, you have the 737-800. One of the last true 'belt and braces' type planes capable of full manual reversion. Theoretically capable of landing safely with no electric or hydraulic power at all. Which means you don't need exotic power back up solutions. Which also means the one battery backup system will only be used to power systems absolutely critical to the continued safety of flight.

There is just no justifying a very basic oversight like this

It is no oversight. It is the correct design decision given the fundamental systems design of the aircraft. Give any half way competent engineer all the facts, and they will reach the same conclusion.

[Patrick AL]

Yet Airbus decided differently?

Give any half way competent engineer all the facts, and they will reach the same conclusion.

Yep! Certainly sounds like Boeing used half-way competent engineers on this!

[Volo]

Yet Airbus decided differently?

Yes - and I would say that in that regard, the Boeing is actually safer.

Airbus is 100% reliant on power. If you don't have at least one functioning hydraulic system, and a little electricity, you are already dead. As a consequence, they are forced to have multiple levels of power redundancy. 2x engines, 1x APU, 1x RAT and 2x batteries. Which means you have a lot of options for backup power to non-safety critical systems.

On the other hand, you have the 737-800. One of the last true 'belt and braces' type planes capable of full manual reversion. Theoretically capable of landing safely with no electric or hydraulic power at all. Which means you don't need exotic power back up solutions. Which also means the one battery backup system will only be used to power systems absolutely critical to the continued safety of flight.

There is just no justifying a very basic oversight like this

It is no oversight. It is the correct design decision given the fundamental systems design of the aircraft. Give any half way competent engineer all the facts, and they will reach the same conclusion.

.......................................

All I know is if I was the manufacturer I would want as much information and for as long as possible in to the accident as the recorders could give .
For starters some information might just dispel speculation as to the causes of the accident .

If the recorders had an independent battery / capacitor then we would not be having this debate here.

There just could be a curved ball here in that @ executive level Boeing might not want proof of any aircraft failure to be made known to the regulator .

[Aquila]

Yes - and I would say that in that regard, the Boeing is actually safer.

Airbus is 100% reliant on power. If you don't have at least one functioning hydraulic system, and a little electricity, you are already dead. As a consequence, they are forced to have multiple levels of power redundancy. 2x engines, 1x APU, 1x RAT and 2x batteries. Which means you have a lot of options for backup power to non-safety critical systems.

How is this different from other aircraft made by Boeing such as the B777?

On the other hand, you have the 737-800. One of the last true 'belt and braces' type planes capable of full manual reversion. Theoretically capable of landing safely with no electric or hydraulic power at all. Which means you don't need exotic power back up solutions. Which also means the one battery backup system will only be used to power systems absolutely critical to the continued safety of flight.

The A350 can lose both of its hydraulic systems and land safely with the use of its EBHA's and EHA's

There is just no justifying a very basic oversight like this

It is no oversight. It is the correct design decision given the fundamental systems design of the aircraft. Give any half way competent engineer all the facts, and they will reach the same conclusion.

Are you saying that other manufacturers have less competent engineers? The reasons for my questions are that you make very interesting claims, such that one aircraft manufacturer designs safer aircraft than the other. My original question before this post was if all manufacturers had to play by the same rules, why would some decide to "over" engineer the system and others decide to follow the rules exactly. Nothing less, nothing more?

I also read that some posts indicate that later models of the aircraft does have a backup power source to the recorders. Why was this change made if you reckon it was unnecessary?

[20048]

How is this different from other aircraft made by Boeing such as the B777?

Every prior Boeing model had manual reversion, with actual mechanical control of elevators and ailerons. No hydraulics or electrics required to operate them.

From the 777 onwards, system design is similar to airbus.

The A350 can lose both of its hydraulic systems and land safely with the use of its EBHA's and EHA's

But it those still require electrical power - hence 2 additional levels of backup power supply on Airbus aircraft.

Are you saying that other manufacturers have less competent engineers?

No. I am saying some armchair commentators on this thread are likely not competent engineers. Airbus engineers given the same fundamental system design and regulatory requirements of the 737-800 would almost certainly have produced the same CVR and FDR design as Boeing engineers did.

I also read that some posts indicate that later models of the aircraft does have a backup power source to the recorders. Why was this change made if you reckon it was unnecessary?

It became necessary because the regulatory requirements changed. Boeing did not modify the system design - instead got Honeywell to produce a CVR with built in battery backup instead.

This upgraded CVR was made available as a retrofit on older models, but I don't think any airline opted to install one (extra cost, weight and a life limited battery to go on the maintenance schedule, etc.). As noted before, these offer no benefit to the airlines themselves, so it is a grudge sale. They will not install them unless the regulators demand it.

[Marno]

I just cannot get used to the idea that cvr's and fdr's can be deemed non critical.

They are an enormous benefit to investigators.

I have also never heard of an airbus where the backup systems failed entirely. Meaning whatever the emergency
It always landed with whatever backup system available in an emergency. (Provided the aircraft was still able to glide)

The weight can be considered balast.

[dollar]

I work with basic machinery but still get surprised and confounded by unusual combinations of events that have lead to unanticipated consequences. This with basic stuff!

From what I've seen of the description of the layout of the 737's electrical system it would take a very sharp person considerable effort to understand it 100%. It's by no means trivial. The design obviously makes certain assumptions, like for example, if both engine generators are gone then there is going to be an APU? The stuff that works off battery is culled back to essentials that enable the aircraft to fly - for as long as possible. Think Atlantic Ocean. The problem was addressed tho - self powered recorders. But it's a retrofit so many planes don't have them. Fate looked for the gap and found it.

[Vogoff]

It is no oversight. It is the correct design decision given the fundamental systems design of the aircraft. Give any half way competent engineer all the facts, and they will reach the same conclusion.

I don't entirely agree. Okay, I agree that it was very unlikely to be an oversight and that the engineers would have dealt with multiple considerations. But I suspect in this case you will find engineers reaching a number of differing conclusions given the same facts - it depends what they choose to prioritise.

What makes the decision odd for me is that this is a component that is only required when everything has gone wrong. It needs to be given the best chance of working when everything else has failed. I think it was only be a matter of time before a complete electrical failure exposed this issue, and apparently the regulators agreed (no doubt with some nudging from the manufacturers of the black box).

That said... we need to recognise that battery management technology has come a long way in the past decade. Even ten years ago batteries would have been big and unreliable and maintenance intensive. Not to mention a CVR and FDR may well become useless when the power goes down - sure they keep recording the signal but there may be nothing to power the recording devices... So I can fully appreciate that engineers would have chosen to skip the batteries because of the cost and complexity that fixing the whole system would have required.

Technology marches on. These days the EFIS fitted to many GA aircraft have their own built in battery backup - because it is now easy to do. But this wasn't always the case, something many ELT owners are painfully aware of.

[Ugly Duckling]

The 737 family main battery has been a 40 Ah Nicad battery since day One. It's rated at the 1 hour rate i.e 40 Amps for 1 hour to 20 Volts at 25 °C. The standby electrical system must provide power for 1 hour maximum the enable the aircraft to land safely. Remember that the diversion fuel is 45 minutes max.
The Essential Buss will be powered by the main battery.

[Aquila]

How is this different from other aircraft made by Boeing such as the B777?

Every prior Boeing model had manual reversion, with actual mechanical control of elevators and ailerons. No hydraulics or electrics required to operate them.

From the 777 onwards, system design is similar to airbus.

The A350 can lose both of its hydraulic systems and land safely with the use of its EBHA's and EHA's

But it those still require electrical power - hence 2 additional levels of backup power supply on Airbus aircraft.

Are you saying that other manufacturers have less competent engineers?

No. I am saying some armchair commentators on this thread are likely not competent engineers. Airbus engineers given the same fundamental system design and regulatory requirements of the 737-800 would almost certainly have produced the same CVR and FDR design as Boeing engineers did.

I also read that some posts indicate that later models of the aircraft does have a backup power source to the recorders. Why was this change made if you reckon it was unnecessary?

It became necessary because the regulatory requirements changed. Boeing did not modify the system design - instead got Honeywell to produce a CVR with built in battery backup instead.

This upgraded CVR was made available as a retrofit on older models, but I don't think any airline opted to install one (extra cost, weight and a life limited battery to go on the maintenance schedule, etc.). As noted before, these offer no benefit to the airlines themselves, so it is a grudge sale. They will not install them unless the regulators demand it.

Ah okay, so when you said Boeing is safer, what did you imply by that? It seems you're not a big fan of the modern fly by wire types such as the B777 and B787?

[Patrick AL]

Ah okay, so when you said Boeing is safer, what did you imply by that? It seems you're not a big fan of the modern fly by wire types such as the B777 and B787?

That is just a personal opinion. I *like* the idea of the pilots having physical control of at least some control surfaces.

But I suppose, if you look at it from a reliability engineering standpoint, With 6 different power sources, 3 different hydraulic systems, and 2 different electric/electro-hydraulic backup systems, the failure probability is probably the same or lower than full manual reversion.

But I still like the simplicity of good old mechanical linkages... Call me old fashioned.

[V5 - LEO]

....heard a very fitting statement today - " I only work on something I can see" The guy was refering to an electrical issue.

So am I, love bellcranks, cabels and human power. I do understand the electrical / hydraulic backup / support, but- man I dont trust the power that makes it work, the fairy stardust stuff