Can a 2 engines plane takeoff at MTOW when 1 engine quits,or only at lower weight? [Archive]

MaverickSu35S

11th Mar 2017, 08:02

Hi,

I can't seem to find a certain answer on the internet, so I dare putting this important question here?

For example, are the 2 engine planes MTOW (maximum takeoff weight) defined or calculated as to allow the planes to safely climb out from a very long runway with no obstacles ahead (which allows for the highest MTOW) when one engine quits? Or are there other design limitation which won't recommend a weight higher than MTOW, such as the maximum weight which the landing gear can carry, regardless of being able to takeoff with an engine loss? I personally believe that the highest MTOW should not be higher than it could allow any commercial aircraft to takeoff and safely climb out (at a much lower vertical speed rate though) in one engine, for aircraft with 2 engines as example.

Wikipedia says just that about the MTOW, but other sources say differently, telling that an aircraft with 2 engines may not safely climb out at MTOW if one engine quits, thus the weight must be limited below MTOW, so I still find this general rule unclear. I think that the PART 25 (or JAR 25) regulates the maximum allowable takeoff weight for any aircraft taking into account the remaining thrust available when 1 or more engines fail in order to still have the aircraft safely climbing out with the highest possible MTOW.

For example, can an MD-82 safely climb out when loaded at 149500lbs (the MD-82's highest MTOW) if one engine fails well above V1, let's say, exactly when the pilot starts pulling for takeoff, or they must do whatever possible to reject the takeoff and stop it even with the consequence of hitting ILS poles, etc. (which would be much better than taking off and crashing anyway)? In this kind of circumstance, if I were to choose between continuing to try and lift it off the ground (there is no turning back from this point, so If I made a terrible mistake, I'm done...) or doing whatever possible to brake it even if I have to make an off-runway excursion and having to chose on what obstacles I should hit if obstacles are unavoidable, I'd rather choose this, for there will be much higher chances of surviving rather than daring to takeoff and finding out that the speed will only keep on dropping after liftoff even with one engine screaming at max. RPM and even if I'll try to retract the flaps (but keep the slats out) and fly leveled in order to reduce the drag, the speed would still drop..., that would mean the end!

So, I wonder if the MD-82 for example, with it's tiny JT-8D 217C engines with 21000lbf (maximum for 5 minutes) each would be capable of safely climbing out when loaded at highest MTOW if one engine stops?

Thank you.

FE Hoppy

11th Mar 2017, 10:52

The Structural limit as quoted in the AFM is 1 of a number of things which can limit the MTOW of any aircraft.
For large aircraft (EASA CS-25) there is a general philosophy that the loss of the most critical engine at any time throughout the flight should result in a safe outcome.
So when operating to those rules the MTOW is the lowest of all the limiting weights.
These could be related to the length of the runway or the climb capability on one engine or the ability to clear obstacles in the take off path (one engine) which may require higher climb capability or of course the certified structural MTOW.

john_tullamarine

11th Mar 2017, 10:53

Lots of threads in PPRuNe talk to this topic.

Suggest you run a search on something like "takeoff weight limit" and have a read through the resulting links. Be aware that references to "mass" and "weight" are sensibly similar and relate to the practices adopted by particular States.

However, in addition to FE Hoppy's observations, the 10 second short brief is ..

(a) the certificated (ie TC and AFM) MTOW is the maximum weight for which all the relevant Design Standard requirements can be met. Often the limiting case either will be one of the structural considerations or one of the WAT limits.

The certificated MTOW is just that - regardless of the circumstances, the pilot may not takeoff at a weight in excess of the MTOW. Caveat - the Regulator may authorise occasional higher takeoff weights for special purposes, eg a ferry flight overseas to permit the carriage of additional temporary tankage fuel.

(b) on a day to day basis the MTOW may have to be reduced (and usually is) by one of a range of considerations. Often such a reduced weight limit will be referred to by other terms, eg RTOW (regulated TOW).

These other limits may be performance requirements (eg WAT limits, OEI obstacle climb, AEO/OEI runway distance limits, etc.), system limitations (eg brake energy limit), cruise limits (eg weight limitation to achieve a high LSA AEO/OEI), destination limits (eg runway or climb limit weight plus expected fuel burn).

The number of engines only changes the numbers, otherwise the philosophy is similar.

MaverickSu35S

11th Mar 2017, 14:23

Thank you very much for your replies. I didn't know this forum already had this topic discussed, my bad I didn't do the search, but thanks again for letting me know about the regulations. The only thing I want to know is if the highest allowable MTOW (ex: for the longest runway in the world with no obstacles ahead) for the MD-82 (149500lbs) permits it to continue and takeoff with just one engine.

Best wishes!

Chris Scott

11th Mar 2017, 17:39

Quote (my emphasis):
"The only thing I want to know is if the highest allowable MTOW (ex: for the longest runway in the world with no obstacles ahead) for the MD-82 (149500lbs) permits it to continue and takeoff with just one engine."

At sea-level on a dry runway with zero gradient, certainly. Otherwise the whole concept of MTOW would in practice be meaningless? But, when considering the acceleration phase on the runway, there has to be an airspeed calculated below which it is not safe to continue in the event of an engine failure. The nominated V1 (decision) speed has to take that into account.

KayPam

11th Mar 2017, 18:07

I read about a procedure for taking off with 3 engines on a 4 engine aircraft : full power on the two symmetrical engine, power up of the third engine when speed is enough.

Could it be possible to takeoff from the start with only one engine ? One would need a very long runway, use little power at the beginning (counteract the yawing moment with the nose wheel at first), then increase power gradually while the rudder gains efficiency, and if this allows to reach VMCG then full power can be applied and the a/c should be able to takeoff on only one engine.
Did anyone ever hear about something similar ?

Chris Scott

11th Mar 2017, 18:15

Hi KayPam,

We had that strange discussion recently on another thread (possibly after the B777 diversion into Iqaluit). But I think this OP is addressing legal SOPs, not flights of fancy that, in the past, have often not ended well!

http://www.pprune.org/rumours-news/590429-swiss-lx40-zrh-lax-diversion-iqaluit-3.html#post9662834

MaverickSu35S

11th Mar 2017, 19:09

Right, I forgot about altitude, but logically that should also be taken into account as for reducing the MTOW depending on available engine thrust for a given air density. But as you've said, for a near sea level altitude and for an air of no more than 35 Celsius (cooler air gives more engine thrust), if the plane is way past V1 (as I initially said) and V2 is reached (so the aircraft can safely keep climbing with just one engine), can an MD-82 continue to takeoff when it weighs 149500lbs? That's all I'd like to know.

Thank you;)!

john_tullamarine

11th Mar 2017, 20:48

That's all I'd like to know.

That's a specific AFM question so it will require an answer from someone who can refer to the manual to check. What you really are asking is .. whether the takeoff is WAT-limited below the MTOW or not.

Roger10-4

11th Mar 2017, 22:07

I don't think anyone here can realistically give an answer to that question. It depends on the runway. However, if the runway is not TOPL limiting and the TOPL exceeds the MTOW then yes it can sustain an engine failure after V1 and meet the required climb gradient.

Chris Scott

11th Mar 2017, 23:56

Hi MaverickSu35S:

You forgot to mention altitude, and I forgot to mention temperature!

Quote:
"for a near sea level altitude and for an air of no more than 35 Celsius (cooler air gives more engine thrust), if the plane is way past V1 (as I initially said) and V2 is reached (so the aircraft can safely keep climbing with just one engine), can an MD-82 continue to takeoff when it weighs 149500lbs?"

As john tullamarine has said, and others imply, every take-off has to be looked at as a separate case, using the performance criteria for the MD-82. But as I said, it would be completely pointless to certificate an aeroplane with a given MTOW based on sound structural factors which nevertheless was higher than the maximum weight ever attainable when considering the performance regulations. The latter, by the way, is referred to as the RTOW (regulated take-off weight).

I don't have access to any take-off performance figures for the MD-82, but any aircraft that could not legally take-off at MTOW on a very long, dry, horizontal runway at sea-level in still air with a temperature of +15C (ISA) with no significant obstacles would be a lemon, to say the least. But now that you have stipulated +35C (ISA+20), that is a very different case.

As your MD-82 is already at V2, the only remaining performance factor will, as john says, be WAT (weight/altitude/temperature). A twin-engine aeroplane, if I remember correctly, must be capable of maintaining a climb gradient of 2.6% ** in still air in the second-segment climb (after gear retraction) on one engine. But don't trust my memory, and you'll need the MD-82 performance charts or tables, and someone who can show you how to interpret them.

** [EDIT] That should have read 2.4%

john_tullamarine

12th Mar 2017, 03:00

Some discussion on gradient here (http://www.pprune.org/tech-log/477551-2-4-regulatory-climb-gradient-single-engine.html).

Bullethead

12th Mar 2017, 06:24

"Could it be possible to takeoff from the start with only one engine ?"

G'day KayPam,

I did it once in the sim after the session was completed and we had a little free time.

How we did it was to use full rudder and nosewheel steering to keep tracking the centreline while slowly introducing thrust on the live engine. Once Vmcg had been achieved then full thrust on the live engine was used with a normal rotate at Vr and climbout at V2, the same as an engine failure after V1 excercise.

The aeroplane was a B767, unfortunately I can't remember the TOW or ambient conditions for this exercise but the B767 climbed away quite nicely at MTOW on one engine.

Cheers.

MaverickSu35S

12th Mar 2017, 09:20

That's a specific AFM question so it will require an answer from someone who can refer to the manual to check. What you really are asking is .. whether the takeoff is WAT-limited below the MTOW or not.

Pinpointed! That's what I'm looking for as well, but the most important was: if the MD-82 would be capable of climbing out when weighing 149500lbs in 1 engine even at sea level and at no more than 30-35 Celsius.

john_tullamarine

12th Mar 2017, 09:36

.. for which you need to refer to the relevant AFM.

MaverickSu35S

12th Mar 2017, 18:04

Thank you! So the AFM should also tell the MTOW in case of one engine out during the takeoff phase.

Cheers!

KayPam

12th Mar 2017, 18:39

john_tullamarine

12th Mar 2017, 22:21

So the AFM should also tell the MTOW in case of one engine out during the takeoff phase.

The AFM provides the tools to do the sums, providing that all relevant external data (wx, runway details, obstacles, etc) are input. The resulting, lowest weight becomes the relevant RTOW for the day.

Obviously not something to be attempted on a regular basis but rather something nice to know, "for science" and curiosity.

A routine and trained for exercise on four-engined machines. Only for interest in the sim, otherwise ... prototype Aero Commanders (May 1951) notwithstanding.

hobbit1983

12th Mar 2017, 22:37

Didn't someone actually do this in a Twin Otter?

john_tullamarine

12th Mar 2017, 22:52

Didn't someone actually do this in a Twin Otter?

There are some stories .. run a search in PPRuNe .. there was a thread I can recall on the subject

.. but the Aero Commander marketing exercise (https://www.flightglobal.com/pdfarchive/view/1951/1951%20-%201050.html) did occur and involved removing one prop and then flying a lengthy OEI flight.

Linktrained

13th Mar 2017, 00:13

S.B.A.C, Show at Farnborough in 1948 (or was it 49 ?) the Airspeed Ambassador did the enire display with one engine feathered. The weight was not given.

( If the weight had been structurally limited by the limitations of an u/c currently undergoing trials, perhaps that one factor would have reduced the MAUW on the day. Just a thought!)

The power available from a nose wheel is greater than that from most tail wheels.

Uplinker

17th Mar 2017, 11:36

Thank you! So the AFM should also tell the MTOW in case of one engine out during the takeoff phase.

Cheers!

Commercial aircraft must be capable of continuing a take-off if the critical engine fails around V1, (and are certified to do so). With a twin engined aircraft, this means they must be capable of continuing the take-off and safely climbing away if one engine fails as V1 is reached.

If on the day, conditions are challenging: very hot or very low pressure, tail-wind or the runway is contaminated etc, or there is challenging terrain on the climb-out, then the aircraft must not be loaded to MTOW but instead the (lower) RTOW. The RTOW is calculated or checked for every take-off, taking the conditions and locality into account, and the aircraft must not be loaded above this weight.

On something medium sized such as Airbus 320 family, on most days from most international airports, the RTOW will be same as the MTOW, but where the runway or the MET conditions are limiting - for example Gibralter - the RTOW can be tonnes less than the MTOW.

vilas

17th Mar 2017, 14:29

Even with ideal Met the RTOW gets limited by LW. MTOW as envisaged here is structural. In ideal condition without any restricting factors OEI is not an issue since it is factored.

john_tullamarine

17th Mar 2017, 21:20

Commercial aircraft must be capable of continuing a take-off if the critical engine fails around V1

ie FAR 25 certifications. The key is the certification basis not whether the aircraft is being used for commercial or non-commercial activities.

On something medium sized such as Airbus 320 family, on most days from most international airports, the RTOW will be same as the MTOW

Depending on the particular aircraft, generally providing that the elevation is somewhere near sea level and the OAT somewhere near ISA. As elevation and/or ISA deviation increase, WAT limits will reduce the weight regardless of runway length, terrain and other considerations.

Even with ideal Met the RTOW gets limited by LW.

This will depend on the difference between TOW and LW and the sector distance. Generally a consideration for shorter sectors.

MTOW as envisaged here is structural.

MTOW will be determined by whatever of the various certification design weight issues results in the lowest weight. Often, but not always, that will be a structural consideration.

In ideal condition without any restricting factors OEI is not an issue since it is factored.

It is not clear what you are referring to here .. perhaps you could amplify your comment ?

vilas

18th Mar 2017, 01:06

n ideal condition without any restricting factors OEI is not an issue since it is factored.
If you see a typical RTOW chart with a long runway, no obstacles in lower temperature range the MTOW matches structural and RTOW caters for performance after engine failure after V1.

john_tullamarine

18th Mar 2017, 09:40

If you see a typical RTOW chart with a long runway,

I think you are saying that WAT limits are the consideration ?

But what is factored in your story ?

vilas

18th Mar 2017, 12:35

I meant if the chart throws up RTOW equal to MTOW then one engine performance is also considered as a part of the calculation. It will be able to take off and meet gradient requirements.

barit1

18th Mar 2017, 13:39

MaverickSU355. . . for a near sea level altitude and for an air of no more than 35 Celsius (cooler air gives more engine thrust), . .

Remember the wings have to fly in that OAT also, so a higher inertial speed (GS) is needed for V1 V2 etc. So higher temp, thrust is less, acceleration is slower, and with a higher GS required, the runway needs to be longer on two counts.

john_tullamarine

18th Mar 2017, 22:02

I meant if the chart throws up RTOW equal to MTOW then one engine performance is also considered as a part of the calculation.

Both AEO and OEI performance is considered for EVERY takeoff. Whichever of the various calculations gives the least TOW for the day becomes the limiting case.

You can't read anything regarding this process into whether the RTOW is equal to, or less than, the MTOW.

It will be able to take off and meet gradient requirements.

This will apply ALL the time, regardless of which limit results in the particular RTOW.

vilas

19th Mar 2017, 05:04

May be factored was wrong choice of word considered would have been more appropriate. Going back to the OP the answer is since there are no adverse factors the answer is simple yes it can take off at MTOW with OEI.

john_tullamarine

19th Mar 2017, 05:28

the answer is simple yes it can take off at MTOW with OEI.

The answer MUST be qualified by something such as "subject to WAT limits".

Pugilistic Animus

20th Mar 2017, 10:52

In the scenario described if Max ToW is equal to the RTOW then the plane would be ok to takeoff provided appropriate WAT limits apply for the following
1. Obstacles

2.second segment critical climb

On a particular runway
WAT limits for the ASDA, TORA and TODA and NTOFP must be met if they are, then RTOW can match MTOW

Uplinker

25th Mar 2017, 18:12

As TangoAlphad also picked up on, the OP is obviously not a pilot ! If s/he was, s/he would know the answer to their question.

Hence why quoting FAR 25, and WAT limits etc is probably too much detail for them and why I gave a very simple generalised answer.

Tango probably explained it better than I did.

Fabo.sk

26th Mar 2017, 17:50

In the end we can all just fall back on the simple logic... no point of certifying a structural MTOW that can not be used as RTOW in normal (i.e. not extremely favourable) conditions.
That'd just be flushing money down the drain.

Linktrained

26th Mar 2017, 23:48

The Ambassador mentioned in #23 in 1949 took off in front of the crowd,using but a fraction of Farnborough's long runway. WAT limits may not have made things difficult.

Blackbushe was near and available. It was used on the days for Guests,(like my employer ) rather than get in the way of the SBAC show. IIRC, after landing the Ambassador did a short single engine reverse taxy.

Little performance information other than " The Limitations" would be made available to me as a F/O or as a Captain until 1962 when the airline which I joined had bought a Photocopier before their first aircraft !

physicus

27th Mar 2017, 02:08

john_tullamarine

27th Mar 2017, 02:12

I'm surprised to see that not a single one of you commenters here is using mass.

In industry practice, both terms are used interchangeably, albeit incorrectly. Functionally, it matters little .. just a little "g" here and there in the equations ..

But you are quite correct, we should refer to mass. I don't see that happening across the board any time soon, though.

underfire

27th Mar 2017, 06:26

Going back to the OP the answer is since there are no adverse factors the answer is simple yes it can take off at MTOW with OEI.

Are you kidding, I certainly hope so.

First off, the criteria has NO CRITERIA OEI DEP It is up to the airline to determine what the take off weight is, by looking at runway length, engine performance (which varies in time), elevation, and especially temperature.

MTOW listed, is based on engine performance (new), the airport at sea level, at 15 degrees C. Vary the engine, altitude, or temperature from 15, and it varies significantly.

Luckily, back at HQ, the performance people who are loading the ac have this sorted out for both DEP, DEP OEI, ARR, and ARR missed.

Do you also feel that you can simply use the same DEP procedure when OEI?

Are you aware that there is no criteria for OEI flightpath (see above) and that simply using what is on the chart (unless spec as OEI) offers no protection unless you can meet that climb rate, to which the pilot does not have the means to calculate?

Eddie Dean

27th Mar 2017, 06:26

megan

27th Mar 2017, 06:44

Single engine take off in a BK117CFolks are talking fixed wing here. Approval for single engine helo ferry could be obtained. Boss did it in an S-76 retrieval from offshore rig.

Bullethead

27th Mar 2017, 08:02

All the airliners I have flown have the limiting masses expressed as weight i.e. MAUW ZFW RTOW MLW MTOW etc. because the guys that fly them are pilots and not physicists.

Procrastinus

27th Mar 2017, 08:26

With a long enough runway, virtually all things are possible!
But is it practical? - that's another thing!

Uplinker

27th Mar 2017, 10:43

When I did my ATPL in the early 1990s, we spoke of MTOM - mass - not weight, as weight is a function of mass and gravitational force. So both from an engineering and physics perspective, speaking of mass is more accurate than weight which varies depending on your location (albeit by tiny amounts). I'm surprised to see that not a single one of you commenters here is using mass. Has this changed in the syllabi to use weight?

Again, given the basic nature of the OP's question, it did not seem worth adding extra unnecessary detail. In aeroplanes taking off from Earth, we are working against Earth's gravity, so weight is the parameter we are more concerned with. (W = mg).

If you fly into orbit, or to the Moon, then yes there will be a huge difference between mass and weight, but I would suggest that is far too much detail in the context of the question?

john_tullamarine

27th Mar 2017, 12:00

With a long enough runway, virtually all things are possible! But is it practical? - that's another thing!

It appears that I'm fighting a losing battle here ... however, for the benefit of the new chums whom I don't wish to get quite wrong ideas, I shall continue ..

In determining the maximum weight permissible for a given set of circumstances, we have to run a bunch of sums covering a range of things, including runway, obstacles, WAT, etc., etc.

For those who haven't run the AFM calculations by hand to see just what is involved it can seem that it is a bit straightforward .. ie just look up the RTOW chart or feed some numbers to the computer and read off the answer.

Just having a long runway doesn't cut the mustard unless the other bits are looked at in detail as well. Whichever of a bunch of limitations gives the lowest weight becomes the limiting case for the day ...

AerocatS2A

27th Mar 2017, 12:01

Are you kidding, I certainly hope so.

First off, the criteria has NO CRITERIA OEI DEP It is up to the airline to determine what the take off weight is, by looking at runway length, engine performance (which varies in time), elevation, and especially temperature.

MTOW listed, is based on engine performance (new), the airport at sea level, at 15 degrees C. Vary the engine, altitude, or temperature from 15, and it varies significantly.

Luckily, back at HQ, the performance people who are loading the ac have this sorted out for both DEP, DEP OEI, ARR, and ARR missed.

Do you also feel that you can simply use the same DEP procedure when OEI?

Are you aware that there is no criteria for OEI flightpath (see above) and that simply using what is on the chart (unless spec as OEI) offers no protection unless you can meet that climb rate, to which the pilot does not have the means to calculate?

He did say "no adverse factors". All of your objections basically amount to "adverse factors".

If you can't take off at MTOW, sea level, ISA, and meet the certification OEI gradient then what use is the MTOW?

As an aside. Some aircraft take-off performance calculations start from a figure that is above the max structural take-off weight so that, after allowing for performance penalties, you can still use the MTOW.

john_tullamarine

27th Mar 2017, 12:07

Just as a minor side point, MTOW is not necessarily a structural limit.

For instance, the GAF N24A MTOW was OEI climb limited and, I am sure, there will be others - the updated MTOW exercise quite some years ago for the Shrike, likewise, was OEI limited.

Caveat, it was quite a while ago that I was last involved with N24 flight tests so I am presuming that things haven't changed for the model.

AerocatS2A

27th Mar 2017, 12:13

Yes that was poorly worded. I used to have the pleasure of flying a Shrike. We had a different MTOW for VFR and IFR. Used to depart VFR then upgrade to IFR after an hour or so. Before that we used to just go IFR for the whole flight but make sure we departed in VMC. Someone decided that wasn't quite kosher.

john_tullamarine

27th Mar 2017, 12:31

Someone decided that wasn't quite kosher.

Indeed .. VFR/IFR had different OEI climb requirements for certification .. VMC was irrelevant. The difference in certification requirements at the time between the FARs and the ANOs caused folks a lot of confusion and head scratching .. but, for the Shrike (and some other Commander models) gave a nice increase over the US limit. As a side line point, the weight increases were largely substantiated by comparison to larger airframes with largely the same structures .. anything different had to be upgraded to suit.

Like you, I have quite a few most enjoyable hours in a bunch of Shrikes .. just like sitting out on a springboard at the local swimming pool.

I recall one flight at EN, many years ago and with a wry smile ... one of the local junior instructors came along in the RHS for the ride. In my normal manner of running checks whilst taxying along, the aircraft started wandering a little off the taxy line. Buggalugs, thinking to help out, but without discussion, stomped on the rudder to bring it back into line .. not the usual way to discover how the NWS worked. As I recall, I raised my eyebrows just a little as his face turned a bright red.

Pugilistic Animus

28th Mar 2017, 12:55

I hate when people use "mass" ultrapretentious

No Fly Zone

28th Mar 2017, 17:04

An amusing discussion, eventually incorporating most of the important points. Save the Most Unusual circumstances, below a conservative(*) V1, STOP. Screw the brakes, just STOP. Above V1, you GO, execute MAX THRUST if necessary, fly the GA procedure and get that thing back on the ground. (Operations and maintenance will sort out the details,, later. In the instant, your ONLY responsibility is to return the airplane to terra firma and without hurting anyone.
The MTOW, distance and performance tables already include a modest fudge factor. Smart pilots double their fudge and never push the edge. They are still flying. Those who may have posed a bit too hard are dead. As is always the case, the Capt. is the ultimate judge and No Carrier will second-guess an AC who says, "No, I won't fly this leg" This is not about tanking some extra fuel - rarely questioned - but pushing the limits of the RWY and departure route. The smart girls and boys simply do not do it. Replacement crew? Smart ones ask why the priors declined and usually agree.
Even with three engines on a two engine airplane, you cannot fly it out of the sea, a lake, a river, or even a ditch! Smart pilots do not gamble.

barit1

28th Mar 2017, 18:05

I hate when people use "mass" ultrapretentious

It was Sir Isaac: F = M * a

Or in the TO case: a = F / M

;)

galaxy flyer

28th Mar 2017, 20:21

barit1

Exactly, but until lunar ops becomes standard, weight equals mass.

galaxy flyer

28th Mar 2017, 20:32

In days past, flying Mr Boeing's Tri-motor, Eastern had lots of flights out of KFLL. The 9s were considerably shorter than presently and a rail track passed just off the end. There was a weight correction for "train on track" to account for a box car. As luck would have, I engineer'd a number of those flights, being tropical (for the US, anyway) just prior to sunset, temps were about 84-ish, with a light east wind, during the winter vacation rush, loads were heavy. It was common to have the manifest include "2 children in arms", some of the wind and a temp one degree less than the ATIS prior to pushback to get a legal RTOW. "Get the TEMP and the WIND prior to going, Captain".