Questions and Answers

I’ve been getting a number of questions from readers lately…some general in nature and some pretty specific.  I thought it might be fun to post some of the questions and my responses to them.  If you would like to submit a question, there’s a button in my profile you can use to send me an email.  If I post your question, all personal and identifying details will be removed.

The following questions are from a guy flying an MD80 simulator on his home pc:

Question: Ground Power (GPU) vs. APU power. Which one do you use more often?  It is my thought that at some point before the flight, you need to use the APU for bleed air supply to start the engines.  Do you just leave the APU on all the time on the ground or do you turn it on just before engine start?

Answer:  Pre-Conditioned Air (PCA) is usually available to heat and cool the aircraft on the ground, so we typically use ground power and PCA until about 15 minutes before departure.  Sometimes PCA is unavailable or the unit does not provide a sufficient amount of air to heat or cool the jet, in which case we leave the APU running the whole time we're on the ground. At about 15 minutes prior to departure, we start the APU to provide the air we need to start the engines.  If the APU is inop, a start cart is used to provide the air we need to start the engines.  The start cart is also capable of providing the air needed to run the air conditioning system if both PCA and the APU are inop or unavailable.  The APU burns approximately 200 pounds of fuel per hour, so it is economical to leave it off as long as possible.

Question:  What kind of reserve fuel do you plan on. When flying in the sim in the MD82 I try to land with no less than 7k lbs of fuel. What do you guys shoot for in the real world?

Answer:  Generally, I like to land with at least 6,000 pounds.  We are regularly planned to arrive with around 5.8 on a good day with no expected delays, but most Captains will rarely accept less than 6.  The legal minimum for an MD80 is about 4.3 (45 minutes of fuel), which in my opinion is nuts.  Our manual does not even allow a go-around with less than 5k, so why on earth would I accept any less.  The problem with accepting less than about 6k is that if something goes wrong at the last minute, you may not have the fuel to divert to even a close airport.  A diversion to an airport less than 20 miles away could easily consume 2000 pounds of fuel.  Also, the flight plan does not consider many of the fuel sucking variables that we encounter every day.  All that said, 6k is about as low as I like to go…thankfully most of the Captains I fly with agree.

Question:  I sometimes use a simulator program called topcat which produces Vspeeds and t/o and landing data for fs. Do you use a real world software program to determine these or do you use paper charts in reference to OAT and weight?

Answer:  We get two things from dispatch before our flight...a Flight Plan and a Departure Plan.  The Flight Plan has all the en-route info we need and the Departure Plan tells us everything we need to takeoff.  The Departure Plan provides settings for flaps, CG, trim, power and V speeds and is good for the planned departure weight plus 2,000 pounds and planned temperature plus 2 degrees.  If we close out 2,001 pounds over the planned weight or if the actual temperature is 3 degrees above or below plan, then we must get new numbers.  After we push away from the gate, we get a “closeout” over the ACARS that provides actual weight, CG and trim settings for takeoff.  If, for some reason, we are required to get new takeoff data or the Departure Plan does not provide data for the runway in use, we can get new data over the ACARS while we taxi to the runway.

Question:  I am kind of confused about the landing speeds. I’ll get a Vapp and a Vref speed and normally shoot to be at Vapp speed at 1000ft then slow to Vref at 300 feet? How do the pros do it?

Answer:  (Thanks for the “pros” comment by the way).  We bug the min maneuver speeds for each flap configuration and then bug approach speed.  Specifically, the top bug is the minimum speed to fly with a clean wing…flaps and slats retracted.  The bottom bug is Vref.  That way, as you begin to slow for the approach, you know as you approach a bug on the airspeed indicator that you need more flaps.  It is always a good idea to extend flaps closer to the min maneuver speed than the max speed for the flap setting to reduce stress on the flaps and the airframe. 

I generally cross the final approach fix between 170 and 180 knots with flaps set to 11 degrees...anything faster than 180 and you will almost surely have trouble being configured in time to be stabilized at 1000 feet.  If you are not stabilized on speed, on glide path with the engines stabilized at approach thrust by 1000 feet above touchdown, a go-around is required.  At about 1800 feet above touchdown elevation, I reduce the throttles to idle, lower the flaps to 15 and drop the gear.  As soon as the gear is down I lower the flaps to 28 then flaps 40 as we slow.  I then push the throttles up to around 1.3 EPR and stabilize at about VREF plus 10 knots.  This all allows me to be fully configured by the 1000 foot requirement.  I then fly VREF plus 10 knots until the flare.

I hope you find this information helpful.  Good luck with your sim.

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Close Call

The picture above is Pacific Southwest Airlines (PSA) flight 182, a Boeing 727, after a mid-air collision with a Cessna 172 over San Diego, California on September 25, 1978. PSA 182 was on a downwind leg for runway 27 at the same time that the 172, N7711G, was flying a practice ILS approach to runway 9. After the impact, both aircraft crashed, killing a total of 144 people…135 passengers and crew aboard PSA 182, a student and his instructor in the 172 and 7 people including 2 children on the ground. An additional 9 people on the ground were injured and 22 homes were destroyed.

This accident and other similar incidents gave impetus to the creation of such technology as the Traffic Collision Avoidance System (TCAS), policies like those requiring altitude reporting transponders while inside the airspace surrounding major airports and procedures inside the cockpit and within air traffic control centers that would help prevent such disasters from occurring in the future.

Since it relates specifically to the story I’m about to tell, let me provide a short explanation of TCAS.

The picture above is a good representation of a typical TCAS display. TCAS involves communication between all aircraft equipped with an appropriate transponder (provided the transponder is enabled and set up properly). Each TCAS-equipped aircraft "interrogates" all other aircraft in a determined range about their position, and all other craft reply to other interrogations. This interrogation-and-response cycle may occur several times per second.

Through this constant back-and-forth communication, the TCAS system builds a three dimensional map of aircraft in the airspace, incorporating their bearing, altitude and range. Then, by extrapolating current range and altitude difference to anticipated future values, it determines if a potential collision threat exists.

The next step beyond identifying potential collisions is automatically negotiating a mutual avoidance maneuver (currently, maneuvers are restricted to changes in altitude and modification of climb/sink rates) between the two (or more) conflicting aircraft. These avoidance maneuvers are communicated to the flight crew by a cockpit display and by synthesized voice instructions.

In basic terms, if I am sharing airspace with an aircraft that is not equipped with TCAS, the TCAS onboard my aircraft will tell me to climb or descend to avoid a collision. If I am sharing airspace with an aircraft equipped with TCAS, the systems onboard my aircraft will communicated and coordinate with the other aircraft and our respective TCAS systems will provide instructions to climb or descend to avoid a conflict.

So here we go…Ontario, California to Dallas - Ft. Worth, Texas on a crisp, cool Saturday afternoon in November. We were planning to have a few open seats on our flight home, but non-revs and last minute travelers seem to come out of the woodwork at the last minute and we managed to leave full. We left the gate a few minutes ahead of schedule and began the short taxi to runway 26R for takeoff as I briefed the Captain on the final weight and balance information and ran the taxi and before takeoff checklists.

The departure procedure out of Ontario is far from the most complicated we fly, but it can be a challenge for a few reasons. First, Ontario has a noise abatement procedure that is put in place to minimize the impact of noise pollution in the area surrounding the airport. The MD80 that I fly is not exactly known for it’s quiet engines and is notorious for setting off noise sensors when the procedure is not followed correctly. They don’t just issue the procedure and ask us to fly as quietly as possible, they actually listen.

Many airports around the country have installed noise sensors in the neighborhoods surrounding major airports. If the pilots exceed the allowable decibel level on one of these sensors, the airline is fined. In this case, the procedure calls for an early left turn with the flaps and slats extended to allow for a sharper turn and a reduction from takeoff to climb power at a lower than normal altitude. By itself, not a huge deal.

The procedure is further complicated by the routing and altitude requirements on the SID (Standard Instrument Departure). After liftoff, we are required to make an early and sharp turn to the southeast and proceed directly to the Paradise VOR. Once direct to Paradise, we must be careful to cross 6 miles from the VOR at or below 4000 feet and then cross over the VOR at or above 2700. We then cross the next fix between 4500 and 9000, the next fix at or below 11000 and the fix after that above 6000. It’s all very confusing and a lot to think about in the first few minutes of the flight, especially when you consider the pilots are also retracting gear and flaps, accelerating to 250 knots, running the after takeoff checklists and watching for traffic.

Traffic. It’s that last little thing that has the potential to make this departure so interesting. Southern California and specifically the LA basin hosts a significant number of small, general aviation aircraft sharing the same airspace as large jets easily operating 2-3 times their speed. The LA basin is also home to a number of major airports…LAX, ONT, BUR, LGB and SNA…to name a few. The combination of large jets and small general aviation aircraft operating in significant numbers in a relatively small geographic area makes the possibility of disaster is a very real concern.

I was flying, so after receiving our takeoff clearance, I pushed the throttles up to stabilize the engines, then called for “auto throttle” and allowed the automatic system to set takeoff thrust. We accelerated normally down the runway and the Captain called out V1, Rotate and we were airborne. As we climbed through 100 feet, we received our first traffic advisory from the tower. I don’t know exactly what was going on in the controllers mind at the time…maybe he was distracted by something else…maybe he was previously unaware of the traffic, but I can tell you that 100 feet is an extremely unusual time to receive a traffic advisory. There was a helicopter two miles west of the airport heading east at 1000 feet. That put him directly in front of us, heading right at us, at an altitude we were going to climb through very shortly. Our TCAS called out an audible warning “Traffic, Traffic” to warn us of the target and displayed a solid white diamond shape on the TCAS display that immediately became an amber circle, indicating the increasingly close proximity of the traffic. I elected to begin the turn as depicted on the departure procedure and increased our rate of climb to clear the traffic as soon as possible. As we passed through 800 feet the TCAS once again sounded…this time with the words “Climb, Climb” as the amber circle became a red square and a green arc appeared on the VSI (Vertical Speed Indicator) indicating the rate of climb needed to resolve the event. We continued our turn and climbed as fast as we could with the nose well above the 20 degrees. We safely passed through 1000 feet and could see the helicopter clearly as he passed behind us…much closer than I would have liked. Then as we passed through 1500 feet and were moving away from the target, the TCAS made it’s final announcement… “Clear of Conflict” and the event was over. No more than 20 seconds had elapsed since rotation.

As we continued to climb, we shifted our attention to completing the after takeoff checklist and monitoring the various altitude restrictions on the departure. Approaching the JUMPA intersection, so named for parachute jumping activity in the area (another target to watch for and a story for another day) we received another traffic advisory from ATC. As we passed through 9,000 feet climbing at about 2000 feet per minute, ATC advised us of opposite direction traffic ahead at 10,500 feet. “Advise you stop climb until passing traffic” we were told. I had already started to push the nose over before receiving the instruction and we level off at 10,000 feet just before the TCAS announced “Traffic, Traffic”. By the time I looked down at the TCAS, the target was already a red square on the display and we received our second Resolution Advisory of the day as the TCAS announced “monitor vertical speed” and a green arc illuminated on the VSI indicating that we should maintain level flight or descend to avoid the target.

Level at 10,000 we visually acquired the traffic ahead, a twin engine Cessna 421. As the traffic passed by, the TCAS announced “clear of conflict” once again and two other targets appeared on the TCAS screen, both below us, one crossing right to left and the other crossing left to right, both less than 1000 feet below us. I wondered if they were aware of each other. With the overhead traffic now behind us, we happily continued our climb out of what is almost always a very busy environment on a nice Saturday afternoon. Once above 18,000 we were once again in no man’s land for small planes enjoying visual flight and could once again relax a bit.

Clearly, TCAS was a tremendously important tool to us on this flight. The ATC controller watching over our flight was responsible for separating us from other traffic in the area, the Captain and I were also responsible for separation and were paying close attention to local traffic, and I’m sure the other pilots involved were as well. That said, TCAS provided a level of safety and protection for our flight that was not available in 1978. With respect to the PSA accident over San Diego, TCAS would almost certainly have prevented the collision. While I am saddened by the fact that it took a death count to bring about this change, I am hopeful that those who lost loved ones in this accident and other like it gain some solace in knowing that the death of those they cared for may very likely have saved the lives of thousands.

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