Leaving the landing gear down after take off in a light twin

[Centaurus]

There is a school of thought that it is better to deliberately leave the landing gear down in a twin after take off until the pilot judges he can no longer make an airborne abort on the remaining runway length if an engine fails. It will take longer to accelerate to Blue Line speed with gear hanging out but that is seen as acceptable.

Question: How does one judge whether or not there is sufficient runway ahead on which to make a successful stop. Should instructors be required to demonstrate this procedure and if so, what publication furnishes the official required performance data that covers the overall distance required on wet and dry runways? How about day or night procedure knowing it is more difficult to judge remaining distances at night than in daylight?

The other school of thought is to retract the landing gear as soon as a positive rate of climb is achieved after lift off and accelerate through best single engine rate of climb speed (Blue Line) as early as practical. If an engine fails when airborne and below Blue Line speed, simply land ahead on remaining runway length. Accept there will be a 5-10 second period where an engine failure in that time requires an airborne abort within the remaining runway length. There will however be more runway ahead within which to to stop, than aborting from further down the runway from a higher altitude with gear down.

Comments on either procedure invited.

[Big Pistons Forever]

There is a school of thought that it is better to deliberately leave the landing gear down in a twin after take off until the pilot judges he can no longer make an airborne abort on the remaining runway length if an engine fails. It will take longer to accelerate to Blue Line speed with gear hanging out but that is seen as acceptable.

Question: How does one judge whether or not there is sufficient runway ahead on which to make a successful stop. Should instructors be required to demonstrate this procedure and if so, what publication furnishes the official required performance data that covers the overall distance required on wet and dry runways? How about day or night procedure knowing it is more difficult to judge remaining distances at night than in daylight?

The other school of thought is to retract the landing gear as soon as a positive rate of climb is achieved after lift off and accelerate through best single engine rate of climb speed (Blue Line) as early as practical. If an engine fails when airborne and below Blue Line speed, simply land ahead on remaining runway length. Accept there will be a 5-10 second period where an engine failure in that time requires an airborne abort within the remaining runway length. There will however be more runway ahead within which to to stop, than aborting from further down the runway from a higher altitude with gear down.

Comments on either procedure invited.

For normal takeoff: It is flaps up 20 inches on the brakes, engine check then brakes release. At Vr it is rotate, positive rate, blue line, gear up. Blue line line is maintained until 400 AGL then the aircraft is accelerated to normal climb speed and climb power set. If the there is an engine failure before blueline the automatic reaction is both throttles to idle. If there is a failure after blueline the failed engine is identified and feathered and the aircraft is flown away.

I do not like the the leave the gear down until no runway available method for several reasons.

1) Altitude = life. The airplane will climb better with the gear up. The first few hundred feet AGL is the danger zone.

2) Actually judging when you still have sufficient runway is pretty hard. Most students will IMO leave the gear down far longer then is practicable to return to the runway.

3) To make the runway particularly if it is narrow, the yaw after the engine failure must be perfectly controlled otherwise the aircraft will have to be manoevered back to the runway centerline inviting low level turns, an often deadly scenario.

4) There is reams of human factors research that shows pilots have great difficulty in making quick judgement decisions when under sudden great stress. This is the foundation of the concept of V1. Over time the idea that there was still room for Captains discretion after V1 has been debunked by the fact that late rejects usually end badly, and this is with very experienced pilots. Since someone training for the ME rating is by definition inexperienced I believe teaching a series of predicable actions which are followed for every takeoff produces the safest outcome.

[S-Works]

Nice summary.

[sheppey]

At Vr it is rotate, positive rate, blue line, gear up

There is no need to leave the gear down until blue line airspeed is reached although practically speaking it only takes a few seconds to reach blue line speed after lift off providing the aircraft is flown at the right attitude.

An engine failure right on blue line speed will almost certainly result in a rapid airspeed decrease below blue line due to the instant drag of the windmilling propeller. In any case,blue line means best single engine rate of climb and a typical piston light twin will generally still have a positive gradient of climb below that speed but a less rate of climb.

In fact some light twin POH publish a best angle of climb on one engine as well as best rate of climb and the former speed is usually lower than that for best rate. Blue line is not the be all and end all of light twin performance on one engine.

So blue line as a decision point for selecting gear up becomes meaningless - in other words you are fooling yourself.

Once the gear is retracting, the reduction of drag means the aircraft will accelerate faster towards blue line and this is why the gear should be retracted on reaching a positive indication of climb and not wait until blue line speed. . Pilots of these light twins should accept the fact that the certification rules mean there will always is an uncertainty period shortly after lift-off and the sooner the aircraft is allowed to accelerate through those few seconds of uncertainty, the sooner a safe single engine airspeed is attained and the next phase of the take off climb occurs.

[what next]

Hello!

We teach it this way (in the sense of the original poster, i.e. gear down until a landing straight ahead is no longer possible) simply beacuse most of "our" examiners want to see it that way. Who are we to question the wisdom of our authority? At the low speed of the typical initial climb out of a retractable single or light twin, the gear does not generate much drag anyway.

The whole topic is purely academic, because after their training is finished, most of our students will never again fly an aeroplane that leaves them with the option of landing back on the departure runway once airborne (if they are lucky enough to get a job at all).

Happy landings
max

[Big Pistons Forever]

There is no need to leave the gear down until blue line airspeed is reached although practically speaking it only takes a few seconds to reach blue line speed after lift off providing the aircraft is flown at the right attitude.

An engine failure right on blue line speed will almost certainly result in a rapid airspeed decrease below blue line due to the instant drag of the windmilling propeller. In any case,blue line means best single engine rate of climb and a typical piston light twin will generally still have a positive gradient of climb below that speed but a less rate of climb.

In fact some light twin POH publish a best angle of climb on one engine as well as best rate of climb and the former speed is usually lower than that for best rate. Blue line is not the be all and end all of light twin performance on one engine.

So blue line as a decision point for selecting gear up becomes meaningless - in other words you are fooling yourself.

Once the gear is retracting, the reduction of drag means the aircraft will accelerate faster towards blue line and this is why the gear should be retracted on reaching a positive indication of climb and not wait until blue line speed. . Pilots of these light twins should accept the fact that the certification rules mean there will always is an uncertainty period shortly after lift-off and the sooner the aircraft is allowed to accelerate through those few seconds of uncertainty, the sooner a safe single engine airspeed is attained and the next phase of the take off climb occurs.

The period from liftoff to blueline will obviously occur with the aircraft at a low altitude and over the runway. So if the engine fails the best thing to do is plop it back on the runway. Even if you can't stop by the end of the runway you are in a very survivable situation.

On one thing I am absolutely certain. It is a practical impossible for the average light twin to maintain altitude while retracting the gear and feathering the propeller and then accelerating to blue line. The pathetic advertised SE climb rates of light twins all of which are only in the 200 to 300 ft/min. can only be obtained at blueline airspeed, with the gear and flaps up, the cowl flap on the inoperative engine closed and 5 deg of bank into the good engine. Even a small deviation in airspeed, high or low, will wipe out the climb rate. A good example of this is from the PA 31 -350 POH. If the temp is above 30 C you can not fly the normal 106 kn blueline because the operating engine will overtemp. Instead the POH requires you to fly at 110 knots. This 4 knot difference reduces the climb by 50 FPM or 40 % of the available SE climb rate under these conditions.

As was noted by "whats next", most ME students will never see a light twin again as the next ME aircraft they will be in will have transport category performance. For those folks the concept of gear down until a judgement decision is made as to insufficient runway exists has no relevance to what they will be flying for the rest of their career. I would argue the idea that the takeoff had 2 parts with the first part being a mandatory reject and the second part an intent to continue mirrors how large aircraft are flown in philosophy although not in exact detail.

For those ME students of mine that were actually likely to fly light twins I insisted on two extra upper airwork exercises.

The first is SE climb at various airspeed to highlight how important it was to accurately fly at blueline to get the most climb performance. I would set only climb power on the operating engine to simulate the worst case hot day high weight case.

The second, and here I will use the Piper Seminole numbers (VMC 56kt, Vr 75kt, Vyse 88 kn) involves setting up with the gear down and slowing to 70 kts. Full power in applied on both engines and and as the airplane accelerates through 75 (ie Vr) retarding one throttle. The student is to retract the gear identify and feather the failed engine (I will set zero thrust 5 seconds after the student call for the feather) and accelerate to 88kts without losing altitude. I have yet to meet anybody who can do it. The usual result is my taking control as the airspeed is deteriorating through 70 and the airplane is starting to sink. Even for the good ones who quickly clean up the aircraft find that the aircraft won't accelerate and they soon have to let the aircraft descent in order to stop the aircraft from deaccelerating. Having the aircraft just sit there totally bogged down and going nowhere is a very big eye opener.

The other thing I do is as part of the pretakeoff brief I insist that the student touch each of the controls as he/she is rattling off the drill. Having that muscle memory is extremely valuable when the excrement hits the fan.

A low altitude EFATO in a light twin is a desperate emergency and even after doing everything right you may still have to close both throttles and take your lumps straight ahead. Sadly the real world EFATO's often have a terrible but predictable sequence.

1) Shock freezes the unprepared pilot
2) The aircraft rapidly deaccelerates due to the drag of the windmilling prop and gear
3) The pilot unconsciously raises the nose as the aircraft starts to sink towards the ground
4) The pilot allows the airspeed to drop below VMC and or/stalls and the aircraft rolls over crashing upside down beside the runway.

[sevenstrokeroll]

wow

ok boys and girls think about it this way...first off, blue line is wonderful...but there is also a speed many have forgotten in the light piston twin world...VXSE

Single Engine Angle of climb...its better than nothing!

so...when I was actively teaching in light twins like seminole, seneca and the like...and I was teaching at a 2500 foot strip, so landing straight ahead was not much of an option...at least on the runway.

so...POS RATE/GEAR UP and look for Vxse as your first major checkpoint if you will...and Vxse isn't usually on the asi.

NOW, if you have sucked up the gear and you lose an engine and you MAINTAIN CONTROL and you are losing altitude/speed...you can:


land ahead gear up
put gear down again

and yes..there is an awful second or two, or three where things can really be bad.


So, figure it out...analyze your density altitude and performance and remember you may have to sacrifice your plane to save your life.

I know one friend...owned a Beech twin...old one...pre baron travelair

he shared it with a multi instructor...they did a one engine approach and go around!!!!! lost control...student killed, instructor badly hurt for life.

its decisions...and sometimes you have to make them before you even get to the airport.

the things I would do at sea level that I might not do at 6000' density altitude.

NOw...if I was taking off at Edwards Air Force Base with an 11 mile dry lake in front of me....I might leave the gear down for a few seconds to build up speed.

;-)

[Big Pistons Forever]

Re Vxse. For most light twins the difference is negligible and for some light twins like the Seminole, the Vxse is not even listed in the POH. When the pressure is on you can't go far wrong putting the airspeed needle on the blue line on the ASI and no thinking will be required.:ok:

Oh and Seven, this "boy" has also come up through aviation the hard way.......

[Big_Buddha36]

Hi,

Am I right in thinking that blue-line is a weight dependant speed anyway (I recall exam01 pointing something on this line out to me after my initial ir) and that with less than mauw, vsse is likely to be even slower.

I haven't flown twins for some time now, but I was originally trained on the "no runway remaining" then when I started work it changed to blue-line.

Logically thinking, it makes more sense to get the gear up sooner rather than later. As others have said, by the time you've got the beast under any sort of control, you'll be ultimately off the runway and in those circumstances, a belly landing might be the lesser of 2 evils?

Any thoughts??

Bb

[Chuck Ellsworth]

Do your training in Canada at one of the better known schools and you don't need to worry about the landing gear on a twin while doing circuits.....they teach leaving it down for the whole circuit....

.....that must be the best way because one of the biggest airlines in Canada hires their finished products so I understand.

[mad_jock]

:D Chuck

Glad your back was worried for a bit.

We have the same issue with daft procedures here with our national airline prefered product.

[sevenstrokeroll]

if memory serves, piper seminole has Vxse of 82kias.

but I haven't flown one in thirty years.

so...let me know and see if after thirty years I am right

[Duchess_Driver]

...to leave the gear down until no usable runway ahead - the argument being that it would be better to roll off the runway into the hedge at 20kts. Always found it difficult to judge exactly when that would be - especially when the excrement spools up!

Not sure I'd like the bill for a localiser though!

[mad_jock]

I was taught that as well but....

I can see the point at say Manchester or Filton or the like but anything under 2000m sod it and get as far away from the ground as possible as quickly as possible.

[Tinstaafl]

Depends on the runway. If a performance limiting runway then gear up as soon as positive climb. If not limiting then gear up after reaching Vyse except that if the runway has plenty of length and it's a no-brainer to land back on, then I'll delay gear up until I:
* can no longer easily land ahead, or
* start a turn, or
* have reached a height that is reasonable for asymmetric ops

which ever of the three happens first. Taking off from some of the looooong runways I've seen (common in the US) I think it's a bad idea not to leave open the option of just landing straight ahead if a donk quits.

Selecting gear up is the demarcation between going to land if the engine fails, or attempting to continue. I emphasize 'attempting' because many light twins aren't required to have any +ve climb performance on one engine, no matter what the configuration.

[avconnection]

Anyone under the illusion that they're safe near blue line in an EFATO situation in a light twin needs an eye opener.

Here's a story about a "High performance" light twin:

http://www.atsb.gov.au/publications/investigation_reports/2003/AAIR/pdf/aair200303579_001.pdf

Here's the legal result:

Civil lawsuit begins over Jandakot crash - ABC News (Australian Broadcasting Corporation) (http://www.abc.net.au/news/2009-08-03/civil-lawsuit-begins-over-jandakot-crash/1376898)

Defence opens in Jandakot crash trial - ABC News (Australian Broadcasting Corporation) (http://www.abc.net.au/news/2009-08-10/defence-opens-in-jandakot-crash-trial/1385608)

Judge finds pilot was negligent - ABC News (Australian Broadcasting Corporation) (http://www.abc.net.au/news/2009-11-11/judge-finds-pilot-was-negligent/1137688)

The civil argument being, he should have dumped it back on the ground and not attempt to fly or fly in a straight line to oblivion. Bear in mind, the prosecution won this argument regardless of their obvious lack of understanding of physics and aerodynamic performance.

Don't fool yourselves, if you lose an engine shortly after take off you're chances are slim and if you can't get it to perform, you're to blame, regardless of what you do.

[bookworm]

The last link says that the judge found the "pilot was negligent for failing to ensure the plane was safe to fly". That's a bit different, isn't it?

[A and C]

Having had to do a single engine go-around in a PA44 the post by big pistons is a chilling reminder of the lack of performance the aircraft offered !

I was lucky that the aircraft was gear down at Vyse as I reached my SE committal height so speed was not a problem but the aircraft seemed only to climb due to the curvature of the earth.

[Centaurus]

but the aircraft seemed only to climb due to the curvature of the earth

Don't necessarily blame the aircraft. It could be a combination of other factors. Typically pilot technique. For example were the control movements smooth and coordinated? Harsh control movements create drag. Were the cowl flaps extended when they need not have been for the temperature of the day?
How accurately was the airspeed flown and was excessive elevator control being used - in other words over-controlling.
Were the flaps fully retracted immediately the go-around commenced or was there a few seconds delay before flaps were selected up?

Was the nose raised immediately go-around commenced on one engine when in fact the aircraft will need nose down during the initial go-around in order to maintain the desired speed as drag is removed. In other words the single engine go-around procedure is different to a normal two-engine go around.

Depending on the density altitude at the time, was the mixture full rich on the live engine or leaned to best power which will give you a better rate of climb under certain density altitude conditions.

Any combinations of the above factors will often degrade the rate of climb single engine. Pilot technique and knowledge of these factors is vital.

[Tinstaafl]

Under the US' FARs, there are light twins that are not required to have *any* asymmetric climb performance, only that their performance 'be determined'. That could be determined to be -ve ie downhill at xx ft/min, even with everything done to maximise performance.

Countries that require +ve climb performance will often impose a climb weight limit.

[A and C]

All perfectly correct but 250-300 ft/ min feels like not very much when you are practicing with one engine back at zero thrust............when you have to go around for real with an engine shut down it feels lie it is taking forever to climb !

[A37575]

Some jet transports can only manage 400 ft per minute rate of climb with an engine failure at V1 at take off performance limited by maximum second segment weight limitations. So the PA44 is not that bad after all in a single engine go-around providing the flaps and landing gear are promptly retracted after full throttle on the live engine. And the zero thrust setting on the `dead` engine is correctly set.

Zero thrust on light twins is not always easy to set because it varies and any variance from the correct setting at the time could either give you an optimistic rate of climb or no climb at all. Few POH state the combination of RPM and manifold pressure setting for zero thrust which means it is a matter of guesswork - such as "my instructor told me'

[Big Pistons Forever]

Zero thrust on light twins is not always easy to set because it varies and any variance from the correct setting at the time could either give you an optimistic rate of climb or no climb at all. Few POH state the combination of RPM and manifold pressure setting for zero thrust which means it is a matter of guesswork - such as "my instructor told me'

This is a very good point and IMO most of the time the "training zero thrust" power setting is actually more than zero thrust thus giving the student a false confidence the actual ability of the aircraft to climb after a real engine failure.

[Tinstaafl]

To add to the over-performance problem giving unrealistic performance expectations: how often is multi engine flying training at MTOW? In my experience, not too often. And if the training is in ISA- conditions, how often is a zero thrust setting used that gives ISA+ performance? ISA-10 is rather different to ISA+20.

Finding an accurate zero thrust setting for a particular IAS & density altitude is easy. It just takes a bit of time in the air. Shut down an engine, trim to hands-off at the required speed and then restart without changing the trim. Once the engine is running set its power setting so that the aircraft is once again flying hands-off with the unchanged trim settings.