During Windshear "Don't change flap or gear configuration"
 

Hi, can anybody tell me why I shouldn't raise de gear during a windshear?
I know that changing flap may affect my angle of attack but what is the effect of raising the landing gear?

Thanks.!

Momentary added drag from the landing gear doors opening/closing.
On the 'ole 707-300 straight-pipe, at very heavy weights on takeoff, you could actually see the reduced ROC on the IVSI...I kid you not.:uhoh:

I had an instructor who said leave the gear down so that if there was a possibility of ground contact during the avoidance maneuver there would be energy dissipation through the gear...anyone else?

Both correct, plus there is enough going on during a severe windshear event to need full concentration from all crew. The only relevant action that is essential is to check the speedbrake is stowed.

............................and that perhaps you have all available thrust on your side!!!!

Some types also display a significant C of G change with gear retraction.

As you might notice, 737fan, all suggestions are there, but remember....the MOST important thing is to get the aeroplane headed uphill ASAP, with ALL of the available thrust at your disposal.
Yes, it really is that important...:ooh:

732fan

I'm with 411A on this. On the 747 the selection of the gear up opens the gear doors and significantly increases the drag.

Airclues

Hi all,

Yes, I understand the additional drag produced by UC doors cycling open/closed and some with big CoG changes when the gear is retracted.....but the 737 has none of that......no UC doors additional drag, the nose doors are already open, and there is only a relatively minor change in CoG when the nose gear retracts forward, since the mains move inboard!

Surely in a relatively short time from selecting gear up, there will be some major positive effects on the airplanes' performance upward!

And as we all know from the OFT, and others with some real experiences, that the windshear effects can last for longer than the retraction cycle.

Comments....

Cheers FD :eek:

I would imagine it's easier to have a blanket standard procedure during windshear instead of trying to remember if you are in an aircraft that would create more or less drag in a w/s environment.

It seems to me it might be wiser to treat the windshear escape procedure as type specific. One size does not fit all!

Best regards,

Westhawk

732fan - this thread has become clouded by the 747 gang. Ignore what happens there. For the 737 it is to leave the gear down. I assume from your questions that is what you are asking about. The procedures are laid down for each aircraft and should be followed. That is what you do.

If you ever get to trying 'severe' windshear (hopefully not for real!) in the sim, it is possible that ground contact can occur. On ALL aircraft (leave 707s and DC10s etc out of it), hitting the ground wheels down makes for a better day than wheels up (even if you leave part of your gear on the ground).

Once 'clear' of the shear, the clean-up takes place. Yes the a/c will have a better overall climb performance gear up, but not if it is sliding on its belly in the mud. Forget 'drag' from doors opening and closing etc. Yes it is 'performance degrading' but Flight Detent is correct and that is why the 'cleanup' is delayed until ground contact is no longer a factor. Exactly the same for a potential terrain avoidance manoeuvre. There again, on the 737, the gear is LEFT DOWN until you are clear of ground contact. Even then, if landing flap is extended, it is that that is retracted first as part of the normal accel profile.

The first objective is to get the aircraft away from the ground, the second away from a downburst (the most hazardous form of windshear). Most recovery guidance systems adapt the flight path demand according to altitude to accomplish this. Both activities require swift action, which should not be complicated by lesser drills until at a safe altitude and / or in a safe area.
If you are unfortunate enough to encounter windshear I suggest that there will significant confusion and concern; the best action is to follow well trained procedures. A good example of how do this is here; Windshear Recovery; note that 0.5-1 sec is very important when descending at 30 ft/sec.

Off the top of my head..... havent all the serious windshear events that ended up hitting the ground, been 3 engined A/C....????

BOAC

The original question was not type specific. I beleieve that the procedure is the same on all modern jet aircraft (certainly all Boeings), to leave the gear down during a windshear event. I was only stating one of the reasons for this on the 747, as that is the only aircraft of which I have any knowledge (apart from the VC10).

Airclues

There's a lot of good discussion in all of the preceding posts, all of it true.

Having been around and in the industry at the time that the mechanics of Wind Shear were being understood, and associated Avoidance and Recovery procedures were being developed, the generic procedure for all aircraft, irrespective of transient drag rises during gear retraction, was that the gear would absorb a huge amount of impact energy in the event of ground contact. Given the choice of flying into the ground with the gear UP or DOWN, this writer would firmly opt for the choice of leaving the Gear DOWN.

If it's a Light or Moderate wind shear encounter, Gear UP would undoubtedly be the best option, ground impact is not a factor, but in these cases, the aircraft performance would well cope with the additional drag. In a severe encounter, however, where ground contact is a significant factor, your chances of survival with the gear down are immeasurably higher.

The one generic procedure that befuddles me, is the recommendation to takeoff with the highest possible Flap setting if wind shear is a possibility. In a lower flap takeoff case, with stall imminent, selection of a higher flap setting will then give me increased stall protection. There is at least one recorded case where a Fokker test pilot opted for a lower flap setting, and "saved the day" by selecting the next highest flap setting to avoid ground impact.

Any comments on the latter? :confused:

Regards,

Old Smokey

Yes indeed, if one is clever enough, the larger flap setting at just the right time will provide a 'balloon effect, which might save the day.

Maybe.;) :}

terrain avoidance requirement
 

at our company one type we operate is the b200. we have a phase one titled "terrain avoidance " .

procedure is basically this;

1. to verbally say "terrain avoidance requirement". ( for crew )
2. set max allowable power.
3. 15 degrees pitch up or 100kias .
4. DO NOT TOUCH FLAP or GEAR .
5. monitor performance roc obstacles etc
6. when clear of obstacles accel to max rate
7. clean up accel.... etc

Windshear- firewall power
pnf sets power to firewall or to max temp
flaps/ gear do not touch
a/s 100 kts with pitch attitude as necessary at light weights as high as 35 deg
thru 1500 agl "company toca" accelerate to 140 and clean up
reset power advise maintenance of the overtorque situation
land, deplane and send it to the barn for mtce.
Engines are expensive, a plane crash more so

GPWS alert if unable to visually confirm
Go Around Max power/Flap 17
Positive rate
gear up
TOCA"1500' agl"
Set power after t/o checklist

No. 2 engined and 2 engined aircraft are not immuned to windshear accidents.