Safe to fly in typhoons

I am surprised that there are flights even when it is typhoon 8, given that schools and offices close down, shouldn't flights be cancelled? It is really scary with such strong winds and rain that the flights are still running.

There are a few factors involved:

- Weather is very local. The weather at the airport and where aircraft fly is relevant. You could have good enough weather to fly at one place and not good enough 5 km away. Airports have very good weather forecasting for the relevant period (a few hours ahead).

- Bad weather is localized in time. It can be safe to fly now, unsafe in 30 minutes, and safe again in 90 minutes. HK can have rather fickle weather so these kinds of shifts are not uncommon.

- Strong winds are not as big a problem as wind shear (shifting winds). A steady strong wind is not a big problem except for take-off and landing. In fact, when flying over the North Atlantic, aircraft routinely encounter winds of several hundred kilometers an hour. Thunderstorms are WAY worse than strong steady winds, since they contain fast shifting air masses and lots of shear.

- As typhoons go, this one is not terribly strong. Note that "signal 8" is not a direct indication of wind strength. It is a guideline for precautions that the organizations and the public should take.

- Commercial aviation is incredibly conservative. Most things have a 50% pad factor. For example structural components like wing spars need to handle 150% of the maximum load they will ever be subjected to in service. Required landing runway lengths need to be 50% longer than what the plane could actually stop in. And so on and so forth. Similarly, weather minima requirements are conservative. The limit of what commercial aircraft can handle is never approached in service, only in test flights.

- MOST IMPORTANTLY: In commercial aviation, no one "wings it" (pardon the pun). There are rules and regulations governing when it is "safe" or not. It's pretty black and white. Either it is safe or it is not. If they're flying, it is safe. But they could shut down the airport in an hour. The weather could turn bad (perhaps with wind strength just going over a limit) while an aircraft is taxiing to the runway and it would have to turn back to the gate. It could be as little as 1km/h of wind speed excess (direction across runway also relevant) and all of sudden it is "not safe". And of course there is the aforementioned pad factor.

This discussion came up after the China Airlines plane crashed landed during a typhoon just after the new airport opened. I remember an airline official say that the airport/runway is never closed and it is up to the pilot and or company to make the decision to land or divert. All the airport does is provide as much information as possible about the weather and runway condition, then leave it up to the pilots.

I understand that different companies have different rules about landing and wind speed etc.

Quite. Different companies have different rules. However they must all comply with regulatory authorities where they operate. An airline may have stricter and/or more detailed policies than the regs dictate, but not laxer.



China Airlines flight 642, and indeed the earlier Kai Tak crash of China Airlines 605 are both examples of accidents where the crew tried to land despite all indications being they should not have. It was safe to operate (other aircraft landed safely) but not at the exact times those aircraft were performing approaches. As I mentioned, bad weather is localized in time. It can be safe now, but not in three minutes. That's why aircraft can always go around, divert, etc...


China Airlines 642: On approach the crosswind component was 28knots gusting to 36. Max for the aircraft is 24. At that point the crew should without hesitation have gone around and performed a missed approach. It is much safer to go around and try again (or divert) than to try and force an unstable approach or an approach where the weather minima are not fulfilled.


China Airlines 605: The crew screwed up by the numbers. They received multiple wind shear and glide slope warnings (from the aircraft systems) on approach. The approach was not stabilized. They should have gone around and conducted a missed approach. In the conditions experienced, going around was mandatory as per China Airlines procedures. They touched down beyond the "touchdown zone", meaning they had less runway to brake in. This is another reason they should have gone around. Finally, after touch down, the spoilers were retracted, rendering the brakes less effective.



Note that if the crews had followed the procedures of their airline, the accidents would most likely never have occurred. In other words, it is not unsafe per se to fly during a typhoon. It is unsafe to ignore the weather minima. They are there for very good reasons.


Further note. Even the strongest typhoons in HK are only about the strength of a category two hurricane in the US. It's pretty windy but nowhere near "batten down the hatches and run for the hills because the biblical flood is coming".

Sure, but even the least safe airline in the world is safer than driving a car.

>Further note. Even the strongest typhoons in HK are only about the strength of a category two hurricane in the US. It's pretty windy but nowhere near "batten down the hatches and run for the hills because the biblical flood is coming".


This is debateable (esp. by the folks in Tai O...) In fact typhoons and super typhoons are equal in strength to hurricanes from Beaufort scale 1-5...they're simply different names for a cyclone in different parts of the world...

http://www.diffen.com/difference/Hurricane_vs_Typhoon#Speed_of_a_typhoon_vs._hurricane

http://en.wikipedia.org/wiki/Tropical_cyclone#Hurricane_or_typhoon


It may be true that the Hong Kong 'experience' is less severe because many developed areas here are sheltered by hills...just watch the news about some of the typhoons that have hit the mainland/Phillipines/Burma/Taiwan in less sheltered areas...widespread devastation and flooding on par or more than anything experienced in NA (carribean countries excepted)

Fair enough. And I would agree that HK doesn't get the worst of it.


Let's take Koppu as an example. According to the news, max sustained winds were just under 150km/h. That wouldn't even make it a Cat 2 Hurricane.


Anyway Koppu isn't actually that powerful as storms go. So most of the time flying is fine in those conditions.