View Full Version : Fuel Jettison Question
26th Feb 2007, 15:27
I was having a discussion today with a fixed wing pilot, and we were discussing Fuel jettison in flight.
Now i know in accordance with JAR OPS 3 Subpart G 3.500(a)(6) "Fuel jettisoning is not planned below 1000 ft above terrain" is what it says in the book, here comes the questions:-
1) If after just passing the TDP with a critical unit failure would you need to jettison fuel to manage V(TOSS) for a go around and keeping to the JAR OPS rule above?
2) There are several types of machine (Perf. Class. 1) which can jettison fuel. Having searched the previous thread the following types came to light.
(SA365N, S58T, AS355N, S61N, AS332L1, BO105, Blackhawk, Panther). Is there any other machines that are now in production that have the ability to Jettison fuel?
26th Feb 2007, 16:15
I think, the need for Fuel jettision in the T/O-Phase just after TDP is not recommendable. If calculated correctly, the H/C should continue its flightpath anyway. On the other hand, the loss of weight due to dumping fuel may be not fast enough and youre quite busy in the cockpit at those circumstances.
Some BO 105s have fuel dumping provisions and the Westland Seaking could also dump fuel, f. e. after ditching for getting lighter to achieve a single engine water takeoff. In that case the fuel would be dumped into the water. That was the procedure we used in the navy some time ago, gladfully i did it only in the simulator. As far as I remember, "normal" fuel dumping should have been done at least at 5000 ft AGL ( if possible )
26th Feb 2007, 17:08
I did once have to dump about 4000lb following an engine failure just after takeoff at MAUW on a v hot day in a CH124A. I doubt that we ever got above 300ft AGL and ended up doing a 70kt running landing, using most of the 6000ft runway. Belated apologies to the residents of Sault Ste Marie, but it saved our bacon that day!
26th Feb 2007, 19:22
It's just as you stated; fuel jettison may not be taken into account below 1,000 feet above terrain. For all the helicopters you have mentioned, TDP/CDP will be around 15-20 feet for a Class 1 takeoff and Vtoss within 10 knots of that, so fuel may not be jettisoned to achieve Vtoss. It comes into its own if you have to fly above 1,000 feet for terrain avoidance or to achieve minimum en-route altitude for IFR flight, but may then be permitted to jettison fuel down to a weight where you can achieve Class One en-route performance at MSA (provided you can still carry enough fuel to make a suitable single engine diversion)
26th Feb 2007, 20:17
Do you really want to have a big valve gushing fuel all around your run-on landing, or your crash?
it would be most useful when you are at altitude, and are faced with a drift-down to an altitude below the hilltops. Not much use if the landing site is a long way off, either.
As I recall, jettison was an add-on feature for the BK117, but it was a frangible plate in the bottom of the tank, and once ruptured, the dump didn't stop until the tank was empty.:eek:
26th Feb 2007, 20:35
In a previous (fixed wing) existence we weren't allowed to dump below 6000' over land and 4000' over water and even then only with ATC approval - largely in case there was someone below you that you couldn't see.
Frankly, in most fixed wing single engine procedures the performance is such that you shouldn't need to dump to make the profile and would you really want to start giving yourself another drill to complete when you're potentially pretty busy anyway?
It can also take quite a long time(for example, a 777 dumps at about 2.5t/hr if fuel is in all tank groups and 1.5t/hr if wings only) - if you need to dump 50t to 70t to get to MLW you need to get to dumping area, then dump, then return to the field.
Many people are surprised to learn that not all jets can fuel dump - the 757 being a prime example - anything requiring an immediate return leads you into an overweight landing.
Having said that in my previous company someone dumped fuel and continued to do so until on finals - overland, big airport, beginning with Heath, ending in Row - and noone said a thing!
26th Feb 2007, 22:15
The Sea King also has a fuel dump, with the pipe positioned above the tail wheel.
Crossing the pond once (courtesy of Eagle), a Buccaneer mate asked what the pipe was for. It seemed a Good Idea to explain that it was the fitting for our arrestor hook, which was only used when non-diversion flying in case of a SE run on landing. Like many lies, it took wings, and a lot of stiff wing drivers spent many a beer asking for more details over the next few days :p
27th Feb 2007, 08:35
Some of the S61s I flew had fuel dump. Supposed to be used in the event of engine failure if the old girl couldn't climb. One of our number on this forum and myself used it one day to get our landing weight down for landing on a platform in a very hot climate and forgot to switch it off.
Dropping 500lb of fuel on a deck is not popular:O
27th Feb 2007, 14:59
Question edited as per suggestion from Sliding Doors....Because i can't formulate myself properly today...to "Some helicopters are fitted with a fuel jettison system, under what circumstances would a helicopter need to use this?" :)
Doesn't the S-92 have the Jettison feature, or is that an optional extra from the factory? I guess when you have 19 Pax and one engine, it's a busy cockpit :suspect:
Thanks for the replies so far :D
27th Feb 2007, 16:26
I think that you are getting confused
One definition for VTOSS is 'For Category A rotorcraft, VTOSS, is a referenced airspeed obtained after lift-off at which the required one engine inoperative climb performance can be achieved. VTOSS assures a steady rate of climb of 100 feet per minute with the landing gear down and the remaining engine operating within approved operating limits'
A quick look at some performance charts will show that when the variables are input you calculate one figure that is both maximum takeoff AND landing gross weight. Fully fuelled is too ambiguous a statement category A (Group 1 Ops) involve calculating an acceptable take off weight. Too heavy and you're no longer Group A.
Perhaps a better question would have been ' Some helicopters are fitted with a fuel jettison system, under what circumstances would a helicopter need to use this?'
Fixed wings are an entirely different beast.
27th Feb 2007, 16:29
Merlin has a fuel dump, and transfers
27th Feb 2007, 16:47
I knew what i meant, just had a problem connecting the right thoughts to the keyboard. Thanks for suggesting the question, which i thought i was asking...if that makes sense. :suspect:
27th Feb 2007, 17:37
Many years ago I used to fly the Wessex on UK SAR. This was also fitted with a fuel dump which was used reasonably frequently in that role. The aircraft would be on standby, fully fuelled and in that state would have a limited payload. As our main operating area (Snowdonia) was only a few minutes flight away, we would often be faced with high winds / turbulence / multiple casualties / MRT members and a helo at close to MAUW. Under those conditions we would often dump fuel to make things more comfortable. Usually this was a non event, but I did have one occasion on a very cold winters night when the fuel didn't vapourise on the way down and had some very confused locals wondering why it had started raining Jet A1 !!:\
27th Feb 2007, 18:07
Lynx used to have an occasional uncommanded engine oil dump..............
Let's assume that we are talking about Commercial Air Transport and JAR-OPS 3.
Category A procedures have a profile consisting of four main parts:
From the hover to TDP; requirement for sufficient surface to permit a rejected take-off
From TDP to TODRH; requirement for sufficient space to permit acceleration to a point where the helicopter achieves Vtoss and a positive rate of climb at 35ft above either, the take-off surface, or all obstacles
From TODRH to 200ft; at Vtoss a rate of climb of at least 100ft/min (followed by a short segment permitting an acceleration from Vtoss to Vy)
From 200ft to 1000ft; at Vy a rate of climb of at least 150ft/minThe take-off mass should permit all aspects of this profile; as a guide it can be assumed that: the first part is flown at the 30 second power setting; the first segment at the 2 minute power setting; and the second segment at the 30 minute power setting.
In fact with modern helicopters, the first segment is seldom limiting and some helicopters can reach 1000ft within the 2 minute power setting - whether this is achieved at Vtoss or Vy is dependent upon the required gradient/angle of climb to achieve obstacle clearance and whether entry into IMC is required (because Vtoss is usually less than Vmini).
Operations in PC1 require that all obstacles in the take-off flight path(defined as the “vertical and horizontal path…from a specified point in the take-off to 1000ft above the surface” - the specified point is that which defines the start of the first segment) are cleared by 35ft (plus 1% if it is flown IMC).
As stated by others; unlike fixed wing, a helicopter is rarely limited by the landing mass at a site just used for take-off.
Fuel dump is reserved for the en-route section and is usually used when: “The presence of obstacles along the en-route flight path may preclude compliance with JAR-OPS 3.500(a)(1) at the planned mass at the critical point along the route. In this case fuel jettison at the most critical point may be planned, provided that procedures in AMC OPS 2.255 paragraph 3 are complied with”the reference to 3.255 is to ensure that, following the fuel dump, there is sufficient fuel to reach the planned destination or a suitable alternative with reserves intact.
Fuel dump should not be used in other than the en-route section.
28th Feb 2007, 04:25
Back in the 80s we were operating S61s with fuel jettison in what the CAA chose to call "Group A Fuel Jettison" but was really Group B ops in disguise. The flights were permitted on the basis that we carried out some tedious calculations to ensure that:
a. as Jim said - you had enough fuel remaining to get to your alternate
b. The fuel require to be dumped to achieve Group A en route performance was in the centre tank (plus 150 lbs for the stand-pipe).
Notwithstanding the legal niceties if I suffered a catastrophic failure of one engine that compromised the performance of the remaining engine then I would consider dumping fuel at any height provided I was in the speed/RoC/RoD envelope. I would rather explain to my pax why I was about to be censured/prosecuted than have my MD phone their relatives to explain why they weren't coming home. The S61 could dump fuel fast enough to make a difference in the minute or so that you are under most pressure to rescue the situation.
By the way Group A FJ was confined to VFR Ops, daylight only
Asking the p2 to vacate the helio is not an option then ?:sad:
28th Feb 2007, 14:18
Gong back through the mist of time, I seem to remember fuel jettison on the S-61 was to provided to maintain a positive rate of climb after a single engine failure if the departure was actually IFR. As I remember the WAT weight was calculated for VFR, should you have a single engine failure you could jettison down to the IFR weight to maintain the required positive ROC required to altitude? All rather hazy, should have listened to my ground instructor at the time. Only a limited number of 61’s had the mod. Jolly useful and mainly used for other reasons.