Why do prop driven aircraft require more reserve fuel than turbo jet powered in IFR?

[ktrwcm2014]

Under CARs 602.88 (4), it says that prop driven aircraft operating in IFR require 45 minutes of fuel after reaching the alternate aerodrome but in the case of a jet-powered aircraft, it's 30 minutes.

Is there any reason behind why prop-driven aircraft require 15 minute additional reserve fuel? I thought it was somewhat backwards because I'd assume bigger (bit of an assumption but still) jet-powered aircraft to require more fuel for extra margin of safety.

Thanks

[Pilotdaddy]

I think it's because it's factoring in range. 30 mins on a jet vs 45 on a non-jet, I'd assume, is probably similar in terms of range.

[digits_]

I'd assume bigger (bit of an assumption but still) jet-powered aircraft to require more fuel for extra margin of safety.

In absolute terms (liter, pounds) they will likely need more. That's why it's expressed as time. Generally 30 minutes will give you more options in a small jet than 45 minutes in a turboprop. Then again, a small turboprop has way more airports available as a last resort vs a big jet that might only be able to land at a few airports.

It's also more likely the jet has better instruments than the average propeller airplane, reducing the chance you wouldn't make it in to your alternate if you hit unexpected bad weather.

But it does seem to be a tad arbitrary.

[co-joe]

I can't really say for sure, but at 400 kts in a jet half hour takes you 200 nm, whereas 250 kts in a prop jobbie gets you 187.5 nm in 45 minutes, so in a way the jet standard is more stringent. Maybe there's some cruise number TC had in mine for each type of the day where the numbers came out even?

[photofly]

The 605 IFR fuel requirements for jets are:

"where an alternate aerodrome is specified in the flight plan or flight itinerary, to fly to and execute an approach and a missed approach at the destination aerodrome, to fly to and land at the alternate aerodrome and then to fly for a period of 30 minutes, or"

fly for a period of 30 minutes - no restriction on speed or altitude. 30 minutes of low level flight isn't going to be at 400 knots.

How is that interpreted in practice? 30 minutes of high-altitude cruise fuel? Or 30 minutes of low-level flight fuel? Or are they about the same?

[co-joe]

The 605 IFR fuel requirements for jets are:

"where an alternate aerodrome is specified in the flight plan or flight itinerary, to fly to and execute an approach and a missed approach at the destination aerodrome, to fly to and land at the alternate aerodrome and then to fly for a period of 30 minutes, or"

fly for a period of 30 minutes - no restriction on speed or altitude. 30 minutes of low level flight isn't going to be at 400 knots.

How is that interpreted in practice? 30 minutes of high-altitude cruise fuel? Or 30 minutes of low-level flight fuel? Or are they about the same?

You're probably right, but then TC allows us to plan almost 400 nm one engine inoperative cruise for the takeoff alternate calculation, you're certainly not getting that at 5000' ASL either. Climb time especially with 30 minutes of gas is probably almost negligible, that a lot of air in the tanks you'd be doing .80 pretty quickly.

[BTD]

The 605 IFR fuel requirements for jets are:

"where an alternate aerodrome is specified in the flight plan or flight itinerary, to fly to and execute an approach and a missed approach at the destination aerodrome, to fly to and land at the alternate aerodrome and then to fly for a period of 30 minutes, or"

fly for a period of 30 minutes - no restriction on speed or altitude. 30 minutes of low level flight isn't going to be at 400 knots.

How is that interpreted in practice? 30 minutes of high-altitude cruise fuel? Or 30 minutes of low-level flight fuel? Or are they about the same?

You're probably right, but then TC allows us to plan almost 400 nm one engine inoperative cruise for the takeoff alternate calculation, you're certainly not getting that at 5000' ASL either. Climb time especially with 30 minutes of gas is probably almost negligible, that a lot of air in the tanks you'd be doing .80 pretty quickly.

At least for 705, this is the likely CAR that would apply,

Fuel Requirements

705.25 (1) Subject to subsection (2), no air operator shall authorize a flight and no person shall commence a flight unless the aircraft

(a) when operating in VFR flight, carries sufficient fuel to fly to the destination aerodrome and thereafter to fly for 45 minutes at normal cruising speed;

(b) when operating in IFR flight on designated routes or over designated areas as defined in the Commercial Air Service Standards, carries an enroute fuel reserve of five per cent of the fuel required to fly to the destination aerodrome; and

(c) when operating in IFR flight, except when complying with the Safety Criteria for Approval of Extended Range Twin-engine Operations (ETOPS) Manual, carries sufficient fuel to allow the aircraft

(i) to descend at any point along the route to the lower of

(A) the one-engine-inoperative service ceiling, or

(B) 10,000 feet ASL,

(ii) to cruise at the altitude referred to in subparagraph (i) to a suitable aerodrome,

(iii) to conduct an approach and a missed approach, and

(iv) to hold for 30 minutes at an altitude of 1,500 feet above the elevation of the aerodrome selected in accordance with subparagraph (ii).

(2) An air operator may be authorized in an air operator certificate to reduce the enroute fuel reserve required by paragraph (1)(b) where the air operator complies with the Commercial Air Service Standards.

So at the beginning of the flight if you lose an engine, you should have enough fuel to be able to get to 10 000 or single engine service ceiling and still make a suitable airport (likely your takeoff alternate) and do all the holding and 30 min etc. Generally, though not always, your takeoff alternate is closer then your destination. So more often then not, at departure you have enough for the normal flight so that any takeoff alternate fuel considerations are easily met.

However, if you didn’t have enough fuel to get to your TO alternate at 10000 or OEI altitude and approach missed, hold for 30 min at 1500 Agl, you should be adding fuel so that you can.

[BTD]

Just to add. TC doesn’t really let us get a distance. They give you a time (60 min non Etops) to get to your takeoff alternate. Some airlines (mine included) will convert that to a still air distance with TC approval. But in that case it would be shown that you can do it.

[Bajan Pilot]

There is also something called, No Alternate IFR. All you have is 30mins on arrival at destination.

[co-joe]

There is also something called, No Alternate IFR. All you have is 30mins on arrival at destination.

The only outfit I know that uses no alternate IFR flies turboprops out of YVR and they use it every chance they get, I'm sure a few other use it but I’ve never worked for one. Most who have the capabilities still don't take on that risk, especially on long flights.

Basically to answer OP's question, the rules are in fact more stringent with respect to jet aircraft with respect to distance required, but less stringent in terms of time, so it depends how you look at it I guess.

[Bajan Pilot]

I can attest to the fact that Jazz used N A IFR. Operated like that several times during my career there.

[redlaser]

Like most, I would say it has to do with range, also Alternate weather has to be good to be chosen as an alternate, expected time of arrival before and after is taken into account. So alternate weather cannot be marginal.

[Big Bird Anonymous]

What it means is that once you arrive at your alternate, the risk of an unforeseen weather event (snow removal) or other unforeseen issue such as traffic congestion can be somewhat mitigated by having the extra fuel. It's not intended to get you somewhere else (unless that is an option) but give you a chance to have a clear path to the runway. Your only option if the time is insufficient is to declare a fuel emergency.