# How is commercial air travel so safe? **URL:** \ **Category:** Factual Questions\ **Created:** [July 3, 2013, 2:16am UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500 "2013-07-03T02:16:35Z")\ **Posts on this page:** 14\ **Page:** 3
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [July 4, 2013, 11:26pm UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500/41 "2013-07-04T23:26:04Z")
> [@Robot\_Arm](#): > > I know of wind-shear accidents on landing (but none lately); don’t know if it’s ever brought down an airliner on takeoff. Here’s [one example](http://www.fss.aero/accident-reports/look.php?report_key=207). ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [July 5, 2013, 4:01am UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500/42 "2013-07-05T04:01:03Z")
> [@Rocketeer](#): > > 737s don’t have a RAT; they depend on manual actuation of the flight controls in the event of loss of hydraulic power / engine failure. > > Neither do 727s nor 707s. > > Don’t know about Douglas or Airbus planes, sorry. 737s still have some sort of tabs that basically make manual control easier without a RAT or other issues. (Trim tabs come to mind, but I don’t think that’s the correct terminology) ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [July 5, 2013, 4:18am UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500/43 "2013-07-05T04:18:53Z")
Servo tabs. Anti-servo tabs Trim tabs Balance tabs ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [July 5, 2013, 4:24am UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500/44 "2013-07-05T04:24:56Z")
Bar tabs, pull tabs, Tab… ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [July 5, 2013, 6:28am UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500/45 "2013-07-05T06:28:12Z")
> [@Leaffan](#): > > What is the mechanism by which airlines share significant events with one another? In the nuclear industry we share Operating Experience (OPEX) bulletins. These consist of anything and everything that could potentially cause concern, or that have resulted in systemic failure, component failure, or human performance failure. We are required to report certain incidents to our company and to the country’s aviation safety authority (ATSB in Australia). The company shares the information internally and, if necessary, makes changes to procedures to prevent recurrences. The ATSB will monitor trends, investigate serious incidents, and share information and make recommendations. Our company has its own substantial safety department that investigates company incidents. We also have flight data that is recorded for every flight and downloaded. Our safety department reviews this data and investigates any irregularities. E.g., if a high rate of descent occurred at low altitude. This system isn’t perfect as by the time it gets investigated the crew often have no recollection of the flight, particularly if it was a brief deviation on an otherwise mundane flight. > [@engineer\_comp\_geek](#): > > A 747 has four engines. It can lose one engine on takeoff and still takeoff safely. It can lose two engines and still climb (slowly) and fly just fine. If it loses 3 engines it will have difficulty climbing, but can maintain flight for a very long time and can land safely. That’s a bit simplistic. A four engine aeroplane must be able to take-off, suffer a single engine failure at the most critical point in the take-off roll, and continue the take-off with a net climb gradient of 2%. The engine out departure track must be designed so that the net climb gradient clears all obstacles by 35 feet (50 feet if a turn is required.) There is no requirement to guarantee take-off performance in the event of a second engine failure. This means that in the case of a B747 it can lose an engine and take-off safely, but if it lost a second engine you’re in unknown territory. If the take-off performance was already limiting such that suffering a single engine failure put the aeroplane right on the engine out performance limits and there were any significant obstacles, a second engine failure would probably not go well. On the other hand if the original performance was well in excess of what was required on the day, you may suffer a second failure and get away with it. Once the take-off is completed, a second failure is not such a big issue. As part of our regular simulator checks in the BAe146 (much smaller than a B747 but subject to identical performance requirements) we have to demonstrate an engine failure after take-off followed by an approach and missed approach. We then have a second engine failure and conduct a second approach and missed approach. The missed approach performance requirements for operating on two engines is very limiting and the aircraft weight required to make it work is often not achievable in the real world. So we could do an approach and landing on two engines but we can’t safely lose two engines on take-off and we can’t safely conduct a missed approach on two engines unless we are very light. A side affect of all of this performance stuff is that the performance of a twin jet with no failures is far better than a quad jet with no failures. This is because the twin has to be able to safely lose half of its engine thrust while the quad only needs to be able to lose a quarter of its thrust. Therefore the excess thrust available when all engines are operating is far greater in the twin than the quad jet. > [@](#): > > A 747 will glide roughly 15 km horizontally for every 1 km it loses vertically. So if you are at 10 km (roughly 32,000 feet) it can glide 150 km and land. Yes. In fact jet airliners generally descend from cruise altitude at idle thrust, so every descent is not far removed from a glide descent. Of course there is some residual thrust at idle so it’s a bit better than gliding. > [@bump](#): > > 737s still have some sort of tabs that basically make manual control easier without a RAT or other issues. > > (Trim tabs come to mind, but I don’t think that’s the correct terminology) [Servo tabs.](http://en.wikipedia.org/wiki/Servo_tab) > [@wikipedia](#): > > Servo tabs move in the opposite direction of the control surface. The tab has a leverage advantage, being located well aft of the surface hinge line and thus can deflect the control surface in the opposite direction. This has the effect of reducing the control force required by the pilot to move the controls.[1] > In the case of some large aircraft the servo tab is the only control that is connected to the pilot’s stick or wheel. The pilot moves the wheel which moves the servo tab and then the servo tab, using its mechanical advantage, moves the elevator or aileron, which is otherwise free-floating. With a servo-tab variant named “geared spring tab”, a pilot was able “to maneuver a vehicle weighing as much as 300,000 pounds flying at an airspeed of 300 miles per hour or more”. ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [July 5, 2013, 3:53pm UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500/46 "2013-07-05T15:53:20Z")
> [@engineer\_comp\_geek](#): > > Here’s the wikipedia page about the famous “Gimli Glider”, a 767 that ran out of fuel due to a calculation error and glided to a landing at an unused air field. It shows that a plane losing all of its engines can still travel a fair distance and land: > [Gimli Glider - Wikipedia](https://en.wikipedia.org/wiki/Gimli_Glider) And arguably even more amazing case was [Air Transat Flight 236.](http://en.wikipedia.org/wiki/Air_Transat_Flight_236) This airliner ran out of fuel in the middle of the Atlantic (thru no fault of their own, maintenance had installed the wrong bracket causing a fuel line to break and leak). By sheer luck they had previously diverted a little south to avoid weather, and this just barely put them in range of an Atlantic island airport. Landed dead stick at 200+ knots, blew out all the tires, successfully stopped before reaching a cliff at the end of the runway(!) No serious injuries. Reason (I think) few people remember this is because it happened on August 24, 2001 (i.e. just two weeks before 9/11). ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [July 6, 2013, 1:40pm UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500/47 "2013-07-06T13:40:50Z")
> [@Richard\_Pearse](#): > > [Servo tabs.](http://en.wikipedia.org/wiki/Servo_tab) From the wikipedia article on the 737: > [@](#): > > The primary flight controls are intrinsically safe. In the event of total hydraulic system failure or double engine failure, they will automatically and seamlessly revert to control via servo tab. In this mode, the servo tabs aerodynamically control the elevators and ailerons; these servo tabs are in turn controlled by cables running to the control yoke. The pilot’s muscle forces alone control the tabs. The 737 is the only currently-produced passenger aircraft this size or larger that can operate completely without hydraulics. ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [July 6, 2013, 7:37pm UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500/48 "2013-07-06T19:37:07Z")
Well, we sure had a [good run](http://www.cnn.com/2013/07/06/us/california-plane-incident/index.html?hpt=hp_t1). ☹ ---
**Author:** ![Washoe](https://avatars.discourse-cdn.com/v4/letter/w/ecae2f/32.png) [@Washoe](https://boards.straightdope.com/u/Washoe)\ **Post date:** [July 6, 2013, 7:46pm UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500/49 "2013-07-06T19:46:37Z")
I had the exact same thought. ☹ I see no indication that this is a catastrophic failure of the aircraft, though. The escape ramps are deployed; there’s clearly somebody alive in there. Let’s wait a couple of hours and see what’s what. ---
**Author:** ![Leaffan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leaffan/32/299_2.png) [@Leaffan](https://boards.straightdope.com/u/Leaffan)\ **Post date:** [July 6, 2013, 8:21pm UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500/50 "2013-07-06T20:21:25Z")
Looks like pilot error. The plane hit the runway prematurely and the tail snapped off. Not that I know much about these things. The weather was perfect. Casualties will be low by the looks of things. ---
**Author:** ![Washoe](https://avatars.discourse-cdn.com/v4/letter/w/ecae2f/32.png) [@Washoe](https://boards.straightdope.com/u/Washoe)\ **Post date:** [July 6, 2013, 8:31pm UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500/51 "2013-07-06T20:31:26Z")
It appears the survival rate was very high; maybe 100%. Passengers were texting loved ones from the tarmac. ---
**Author:** ![jackdavinci](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackdavinci/32/3259_2.png) [@jackdavinci](https://boards.straightdope.com/u/jackdavinci)\ **Post date:** [July 6, 2013, 8:32pm UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500/52 "2013-07-06T20:32:06Z")
It’s not safer. There are more fatalities per mile than cars. It’s just that people don’t spend as much time in planes, so it is less likely they will end up in an accident. > **[How Risky Is Flying?](https://www.pbs.org/wgbh/nova/article/how-risky-is-flying/)** > > Harvard's David Ropeik explains why judging risk is a risky business. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [July 6, 2013, 10:01pm UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500/53 "2013-07-06T22:01:23Z")
> [@jackdavinci](#): > > It’s not safer. There are more fatalities per mile than cars. It’s just that people don’t spend as much time in planes, so it is less likely they will end up in an accident. > > [How Risky Is Flying? | NOVA | PBS](http://www.pbs.org/wgbh/nova/space/how-risky-is-flying.html) Ridiculous. The table shows deaths per vehicle mile. Commercial planes carry far more people per vehicle than cars. If you want individual risk per mile, you need to use deaths per passenger mile, which is around [3 per 10 billion](http://en.wikipedia.org/wiki/Aviation_safety#United_States). ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [July 6, 2013, 10:03pm UTC](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500/54 "2013-07-06T22:03:51Z")
> [@jackdavinci](#): > > It’s not safer. There are more fatalities per mile than cars. It’s just that people don’t spend as much time in planes, so it is less likely they will end up in an accident. > > [How Risky Is Flying? | NOVA | PBS](http://www.pbs.org/wgbh/nova/space/how-risky-is-flying.html) There’s so much fail in that article I don’t even know where to begin. ETA: What **Dr. Strangelove** said. [Previous page](https://boards.straightdope.com/t/how-is-commercial-air-travel-so-safe/662500.md?page=2)