Sorry to sound pretentious then! No I'm not, it WAS only a joke...
Information in any flight manual is only a guide. However comrehensive the charts and graphs in the flight manual; experience has shown me that Sikorsky predicted fuel useage figures can be a little over-optimistic.
Specific fuel consumption is expressed as nm/lb. Some FMSs do automatically take the actual fuel flow and give an accurate fuel consumption / air range figure on the fuel page. When flying long offshore SARs (200 nm plus), we used the fuel pages while we compared different altitudes to see if we could improve our specific fuel consumption figure because often every drop counted and we had no diversion. The FMS calculated everything and took into account the wind effect, often the biggest factor for a helicopter.
One simple way of keeping tabs on your fuel is to make up a row & column table showing actual fuel contents, for example in hundreds, on the vertical axis on the left, and fuel flow, again in hundreds, across the horizontal axis across the top. Do the maths for flying times remaining and fill in the boxes.
When calculating my flight times remaining I added in my aircraft minimum landing fuel figure to make sure I didn't forget it (200 lbs in my case). For time to dry tanks, I look two rows up in the same column, i.e. for the actual gauge total indicated at the time of the check plus 200lbs. I added a note to this effect at the bottom of the table so I didn't forget what I was doing.
You can use this in the air either by looking at the fuel flow gauges if fitted, or a timed fuel drop on the aircraft contents gauges.
We are all well-versed in estimating time of arrival so all you need to do in the air is know your required flight time remaining, and check it against your endurance using the table.
Of course all you are doing is the arithmetic in advance but use of my accurate table has allowed me to confidently confirm I was able to continue to a SAR scene without the hassle of landing on an oil rig for a refuel; when you are getting low on fuel you do need to get those figures correct!
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If anyone can tell me how to post an image file I will try to put an example of such a table here.
Last edited by ShyTorque; 13th Apr 2002 at 17:21.