COFFIN CORNER = STALL SPEED INCREASES WITH ALTITUDE + CRITICAL MACH NUMBER DECREASES WITH ALTITUDE

 

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When a jet aircraft captain decides to fly at an altitude very close to the operational ceiling of the aircraft, the risks are increased due to the environment of this flight being within the area called the "coffin corner", which is formed by the apexes of the stall speed curves and the Mach number curve.

Look in the image showing the two Cartesians’ curves almost joining at the top of the curves.

All it takes is gusty turbulence, a steep curve, ice formation, or an incorrect speed adjustment can push the plane against one of the curves, what means very high possibility to lose the jet plane flight controls. 

You must descend gradually [around 1500 feet per minute] to flight level around 25,000 feet to keep the plane at the safety zone of the envelope formed by the two: stall speed and Mach number Cartesian’s curves.

PRIME AIR CARGO OVERRUN RUNWAY 30 AT MIAMI KMIA AIRPORT - BEFORE FULL FLAPS TO VREF RUNWAY THRESHOLD 50 FEET

 BEFORE FULL FLAPS

AIR INDIA FLIGHT 171 - AFTER ENGINE STARTING IN-FLIGH THERE WAS A MAYDAY CALL

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BOEING 787-9 AUTOSTART

Both engines are normally started at the same time, unless the outside air temperature is below 41°F (5°C).

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FROM THE PRELIMINARY REPORT

As per the EAFR data both engines N2 values passed below minimum idle speed, and the RAT hydraulic pump began supplying hydraulic power at about 08:08:47 UTC.

RAT in extended position

As per the EAFR, the Engine 1 fuel cutoff switch transitioned from CUTOFF to RUN at about 08:08:52 UTC. The APU Inlet Door began opening at about 08:08:54 UTC, consistent with the APU Auto Start logic. Thereafter at 08:08:56 UTC the Engine 2 fuel cutoff switch also transitions from CUTOFF to RUN. When fuel control switches are moved from CUTOFF to RUN while the aircraft is inflight, each engines full authority dual engine control (FADEC) automatically manages a relight and thrust recovery sequence of ignition and fuel introduction.

The EGT was observed to be rising for both engines indicating relight. Engine 1’s core deceleration stopped, reversed and started to progress to recovery. Engine 2 was able to relight but could not arrest core speed deceleration and re-introduced fuel repeatedly to increase core speed acceleration and recovery. The EAFR recording stopped at 08:09:11 UTC

At about 08:09:05 UTC, one of the pilots transmitted “MAYDAY MAYDAY MAYDAY”. The ATCO enquired about the call sign. ATCO did not get any response but observed the aircraft crashing outside the airport boundary and activated the emergency response.

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Boeing 787-9 FUEL switches operation demonstrated

To move any FUEL flow control switch from RUN position to CUT-OFF position requires PULLING the switch BACKWARD to pass it over the safety detent and, put it down on CUT-OFF position. It is very hard accidentally the switch moves to CUT OFF position.

Operation illustration for LAYMEN better understanding

BACKGROIUND

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Considering the MAYDAY call a consequence of a very stressful situation on flightdeck. 

So, the first thing the pilots had to pay attention it was the engine parameters out of standard and secondarily, a pilot had acknowledged an abnormal engine.

Following that, the other pilot has perceived an engine having been shut down by his colleague, who denied to have shut down the engine.

We, out of the cockpit, must accept the condition for shutting down an engine. The pilot needs to pull the FUEL switch up (back) to overtake the safety detent and, bring it to OFF position, so the FUEL flow will be cut to the engine.

The FUEL switch has no condition to jump for itself over the safety detent.

Now we have two possibilities:

1.     A pilot mistakenly moved manually the FUEL switch to OFF position. But he denied it.

2. The FUEL switch had lost electric power to keep the fuel flow function (at the RUN position) feeding the engine.

NOTE: There is a COMMON MOTOR STARTER CONTROLLER

The Common Motor Starter Controller or CMSC, supplies variable frequency and variable AC voltage to airplane systems that need a high voltage to operate such as the Cabin Air Compressor and the Electric Motor Pump. Because the CMSC's can get very hot, they are cooled via the Power Electronic Cooling System (PECS).

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FROM THE PRELIMINARY REPORT

All applicable Airworthiness Directives and Alert Service Bulletins were complied on the aircraft as well as engines.

The FAA issued Special Airworthiness Information Bulletin (SAIB) No. NM-18-33 on December 17, 2018, regarding the potential disengagement of the fuel control switch locking feature. This SAIB was issued based on reports from operators of Model 737 airplanes that the fuel control switches were installed with the locking feature disengaged. The airworthiness concern was not considered an unsafe condition that would warrant airworthiness directive (AD) by the FAA. The fuel control switch design, including the locking feature, is similar on various Boeing airplane models including part number 4TL837-3D which is fitted in B787-8 aircraft VT-ANB. As per the information from Air India, the suggested inspections were not carried out as the SAIB was advisory and not mandatory. The scrutiny of maintenance records revealed that the throttle control module was replaced on VT-ANB in 2019 and 2023. However, the reason for the replacement was not linked to the fuel control switch. There has been no defect reported pertaining to the fuel control switch since 2023 on VT-ANB.

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In-Flight Start

In-flight start envelope information is displayed on the EICAS display when an engine is not running in flight (N² RPM below idle RPM) or when an engine is shut down in flight and the respective engine fire switch is not pulled. The in-flight start envelope indicates the airspeed range necessary to ensure an in-flight start at the current flight level. If the current flight level is above the maximum start altitude, the maximum start altitude and respective airspeed range are displayed.

Secondary engine indications are automatically displayed in flight when an engine is not running (N² RPM is below idle with corresponding FUEL CONTROL switch in RUN) or when a FUEL CONTROL switch is moved to CUTOFF. A starter assist indication (X-START) is displayed below the N2 indication if airspeed is below that recommended for a windmilling start. For in- flight starts, autostart makes continuous start attempts until the engine either starts or the pilot aborts the start attempt by positioning the FUEL CONTROL switch to CUTOFF (and positioning the START switch to NORM if it was a starter assisted attempt).

During the windmilling in-flight start, the EEC monitors engine parameters to provide the best fuel schedule to ensure the shortest possible start time. (Refer to Engine In-Flight Start, QRH, Non-Normal Checklists Chapter 7, for the in-flight engine start procedure.)

NOTE: There is a COMMON MOTOR STARTER CONTROLLER

The Common Motor Starter Controller or CMSC, supplies variable frequency and variable AC voltage to airplane systems that need a high voltage to operate such as the Cabin Air Compressor and the Electric Motor Pump. Because the CMSC's can get very hot, they are cooled via the Power Electronic Cooling System (PECS).

Engine start (Dynamic)

Once all doors and hatches are closed, external cables and pipes have been removed and the APU is running, we're ready to push back from the gate and start our engines. 

Both engines are normally started at the same time, unless the outside air temperature is below 41°F (5°C).

On other aircraft types, the engines require high pressure air from the APU to turn the starter in the engine. This requires a lot of power from the APU and is also quite noisy. On the 787, the engine start is entirely electrical.

Power is drawn from the APU and feeds the VFSGs in the engines. If you remember from earlier, these fist act as starter motors. The starter motor starts the turn the turbines in the middle of the engine. These in turn start to turn the forward stages of the engine. Once there is enough airflow through the engine, and the fuel is igniting, there is enough energy to continue running itself.

The electrical system during an engine start. L1 and L2 are in generator mode whilst R1 and R2 are acting as starters. The APU is still providing power to the aircraft systems.

After start

Once the engine is running, the VFSGs stop acting as starter motors and revert to acting as generators. As these generators are the preferred power source, they automatically take over the running of the electrical systems from the APU, which can then be switched off. The aircraft is now in the desired configuration for flight, with the 4 VFSGs in both engines providing all the power the aircraft needs.

As the aircraft moves away toward the runway, another electrically powered system is used — the brakes. On other aircraft types, the brakes are powered by the hydraulics system. This requires extra pipe work and the associated weight that goes with that. Hydraulically powered brake units can also be time consuming to replace.

By having electric brakes, the 787 is able to reduce the weight of the hydraulics system and it also makes it easier to change brake units. "Plug in and play" brakes are far quicker to change, keeping maintenance costs down and reducing flight delays.

In-flight

Another system which is powered electrically on the 787 is the anti-ice system. As aircraft fly though clouds in cold temperatures, ice can build up along the leading edge of the wing. As this reduces the efficiency of the wing, we need to get rid of this.

How pilots keep you safe while flying through strong winds

Other aircraft types use hot air from the engines to melt it. On the 787, we have electrically powered pads along the leading edge which heat up to melt the ice.

Not only does this keep more power in the engines, but it also reduces the drag created as the hot air leaves the structure of the wing. A double win for fuel savings.

Engine generators

Two Starter/Generators 235 Vac (L1-L2-R1-R2)

• Each engine, two starter/Generators are directly connected to the Engine gear box, producing variable frequency power proportional to the Engine rotor speed.
• Both engine starters are used for engine start, but nevertheless the engine may be started with only one generator. The start will be slower than the normal start.
• Power for engine start may be provided by the APU, opposite engine generators or external power.
• Both generators on each side will provide a variable frequency of 235 Vac to the AFT E/E bay, were power is distributed. Four main buses (L1-L2-R1-R2) each powered by its respective generator line. Automatic protection ensures that only one source is applied to the main bus at a time.
• Each generator has a drive disconnect mechanism that allows the generator to be mechanically disconnected from the engine. Depending on the fault condition, can be disconnected manually or automatically. (DRIVE DISC), once disconnected cannot be reconnected.

ABOUT THE LANDING GEAR NOT RETRACTED

The Preliminary Report brought the answer, the landing gear lever was not moved to the UP position after lift off.

The flap handle assembly (fig.11) sustained significant thermal damage. The handle was found to be firmly seated in the 5-degree flap position, consistent with a normal takeoff flap setting. The position was also confirmed from the EAFR data. The landing gear lever was in “DOWN” position. (fig.12)

The thrust lever quadrant sustained significant thermal damage. Both thrust levers were found near the aft (idle) position. However, the EAFR data revealed that the thrust levers remained forward (takeoff thrust) until the impact. Both fuel control switch were found in the “RUN” position. (fig.13) The reverser levers were bent but were in the “stowed” position. The wiring from the TO/GA switches and autothrottle disconnect switches were visible, but heavily damaged.

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In-Air Rat only Mode (Standby Power)

Is active with the loss of all electrical power to the Captain’s & First officers flight instruments, in that case the RAT will energize the captains flight instruments with some essential equipment including flight controls, navigation and communications.

Energized equipment by the RAT are as follows.

Captains inboard & outboard DU’s, lower DU,MCP, PFC, ECL, FMC limited operation, Autopilot limited operation, Autoflight system, Captain’s & First officer’s ACP’s and the flight interphone,        LEFT( VHF/TCP/DSP/MFK/CCD/CCR), LEFT & RIGHT (IRU/AHRU/INR), Centre pitot heat, Engine/APU fire detection and miscellaneous lighting.

INOP systems include TAT, Autothrottle, LNAV/VNAV, FMC predictions and thrust limits, TAP, Flaps & Slats, Stabilizer trim, Packs, HUD’s, HF, SATCOM, TCAS, GPWS, Transponder, WX radar, External lighting, Wipes, and Window heat.

Air India Flight 171 B787-8 VT-ANB – POSSIBLE FAILURE EVENT on Slat Autogap and Slat Pregap

 

FAILURE on Slat Autogap and Slat Pregap

The slat autogap function is only available in primary mode when the slats are in the middle position [FLAPS lever set to 1 position] and the airspeed is below 225 KIAS. At a high angle of attack [seconds before the crash the plane has been seen increasing the nose pitch up], autogap fully extends the slats to increase the wing camber, thus increasing the lift and margin to stall. The slats return to the middle position after the angle of attack decreases [but the nose pitch up was kept]. The autogap trip threshold is a function of AOA, airspeed and flap position.

In the secondary mode the system is too slow to respond to an autogap request, so a pregap function exists. The slats automatically move to the fully extended position from the middle position when the flap lever is not UP and airspeed is less than 225 KIAS. The slats remain in the extended position until the flap lever is in the UP position or airspeed is above 225 KIAS.

Flaps and Slats

The flaps and slats are high lift devices that increase wing lift and decrease stall speed during takeoff, approach, and landing.

The airplane has an inboard and an outboard flap on the trailing edge of each wing, and one inboard and five outboard slats on the leading edge. A two-position Krueger flap provides a seal between the inboard slat and the engine nacelle on each wing.

In the flaps 1 position, only the slats move. Flaps 5, 15, and 20 are takeoff flap positions. Flaps 25 and 30 are landing flaps positions. Flaps 20 is used for some non-normal landing conditions.

Flap and Slat Sequencing

When the flap lever is in the UP detent, all flaps and slats are commanded to the retracted position. Moving the flap lever aft allows selection of flap detent positions 1, 5, 15, 20, 25 and 30. The flaps and slats sequence so that the slats extend first and retract last.

Starting from flaps UP, selection of flaps 1 commands the slats to move to the middle position. The flaps remain retracted.

Selection of the flaps 5, 15, and 20 positions commands the flaps to move to the position selected. The slats remain in the middle position.

Selection of flaps 25 commands the slats to move to the fully extended position. The flaps do not move.

Selection of flaps 30 commands the flaps to extend to the primary landing position.

During retraction, flap and slat sequencing is reversed.

The mechanical gate at the flaps 20 detent prevents inadvertent retraction of the flaps past the go-around flap setting. The mechanical gate at flaps 1 prevents inadvertent retraction of the slats past the middle position.

Flap and Slat Modes

There are three modes of flap and slat operation:

• primary

• secondary

⚫ alternate

In the primary mode, the flaps and slats are controlled together and positioned using center hydraulic system motors. Autogap and flap load relief operate in the primary mode.

The secondary mode is automatically engaged when any of the following conditions occur:

⚫ center hydraulic system failed, or

· flap or slat primary control failure, or

primary mode fails to move the flaps or slats to the selected position, or

• control surfaces travel at less than 50% of the normal hydraulic rate, or

⚫ uncommanded flap or slat motion is detected, or

• flap or slat disagree is detected

In the secondary mode the slats and flaps are controlled separately and can be positioned by hydraulic or electric motors. For example, if the slats hydraulic control fails, the flaps are still driven hydraulically but the slats are now powered electrically. Pilot control is through the flap lever but operation in secondary mode is limited to flaps 20 by non-normal procedures.

The three-position alternate flaps selector extends and retracts the flaps and slats. The flaps and slats extend simultaneously, but slat retraction is inhibited until the flaps are up. Alternate mode flap and slat extension is limited to the slats middle position and flaps 20. Asymmetry and uncommanded motion protection, slat autogap and pregap, and flap and slat load relief are not available in alternate mode.

The alternate mode must be manually selected. Slat and flap operation time in the secondary and alternate modes is greatly increased.

SPOOFING TCAS TRAFFIC ADVISORY & RESOLUTION ADVISORY AT RONALD REGAN NATIONAL AIRPORT (KDCA) - NO AIR TRAFFIC AROUND

UPDATED MAR 13, 2025

HELICOPTER ROUTE 4  NO MORE EXIST

UPDATED Mar 11, 2025

Many TCAS TA and RA on KDCA ARRIVAL and FINAL APPROACH, but NO INTRUDER TRAFFIC AROUND

 

The Federal Aviation Administration is investigating a multitude of Traffic Collision Avoidance System (TCAS) alerts near Reagan National Airport in Washington. Multiple aircraft from different air carriers reported the alerts Saturday while on the River Visual approach.

 

Despite these alerts, no other aircraft were detected nearby. Many aircraft received resolution advisories (RAs), directing the crew to maneuver away from a potential collision.

 

“Several flight crews inbound to Reagan Washington National Airport received onboard alerts Saturday indicating another aircraft was nearby when no other aircraft were in the area. Some of the crews executed go-arounds as a result of the alerts,” an agency spokesperson said in a statement. “The FAA is investigating why the alerts occurred.”

 

One Republic Airways crew reported an RA at around 1,200 feet, adding that “there was something diving straight onto us,” per air traffic control audio recordings. Another PSA Airlines crew said they got two traffic advisories (TA), which warn of a non-imminent collision.

DELTA 4819 CRJ-900 CRASH IN TORONTO, CANADA CYYZ - CROSS WIND GUST

 UPDATED Mar, 22 2025

PRELIMINARY REPORT

Source:

Transportation Safety Board of Canada

Air Transportation Safety Investigation A25O0021:

Preliminary Report (released 20 March 2025).

Transportation Safety Board of Canada 200 Promenade du Portage, 4th floor Gatineau QC K1A 1K8 819-994-3741; 1-800-387-3557 www.tsb.gc.ca communications@tsb.gc.ca

 

 The Transportation Safety Board of Canada (TSB)

 On 17 February 2025

 

CL-600-2D24 aircraft (CRJ-900LR) (registration N932XJ, serial number 15194) was operating as Endeavor Air flight EDV4819 from Minneapolis-Saint Paul International/Wold-Chamberlain Airport (KMSP), Minnesota, United States, to Toronto/Lester B. Pearson International Airport (CYYZ), Ontario.

 

 During the landing on Runway 23, the aircraft impacted the runway, the right wing detached, and a fire ensued. The aircraft overturned and slid down the runway inverted, coming to rest near the intersection of Runway 23 and Runway 15L. Aircraft rescue and firefighting responded, and all passengers and crew evacuated.

All times are Eastern Standard Time (Coordinated Universal Time minus 5 hours).

 

At 12:47 (EST)[ 07:47 UTC]

Flight EDV4819, IFR [Instrument Flight Rules]

FROM: Departed (KMSP) Minneapolis-St. Paul International/World-Chamberlain Airport Minnesota, United States,

TO: (CYYZ), Toronto/Lester B. Pearson International Airport Ontario, Canada

 

POB: 2 flight crew members, 2 cabin crew members, and 76 passengers on board.

The captain was seated in the left seat and was the pilot-monitoring [PIC] for the flight. The first-officer was seated in the right seat and was the pilot-flying (PF).

The crew received clearance for the instrument landing system approach to Runway 23 at CYYZ.

Weather

The aerodrome routine meteorological report for CYYZ issued at 1400 indicated the following:

• Winds from 270° true (T) at 28 knots, gusting to 35 knots

• Visibility 6 statute miles (SM) in blowing snow

• Runway visual range for Runway 24L variable between 3000 feet and more than 6000 feet with an upward trend

• Broken ceiling at 3400 feet AGL

• Temperature −9 °C and dew point −14 °C

• Altimeter setting 29.93 inches of mercury

• Remarks indicated cumulus clouds at 6 oktas

 

14:12:01 (EST) [09:12:01 UTC]

The aircraft descended through 500 feet above ground level (AGL). The aircraft’s indicated airspeed was 150 knots, its ground speed was 121 knots, and the engine thrust was indicating approximately 64% N1.3 The rate of descent was 720 fpm, and the localizer and glide slope were centered. Five seconds later, the PF disconnected the autopilot.

 

Flight controls

The flaps and slats were fully deployed at the time of the occurrence. The flap jackscrew threads were measured to be 10 inches for both the left and right inboard flap actuators (4 locations), which corresponds to 45° of flaps. Based on measurements taken from the left slat, the slats were in a 25° position.

At the time of the occurrence, the aircraft was being operated within its allowable weight-and-balance limitations. The occurrence landing weight was approximately 73 000 pounds, and there was about 6000 pounds of fuel remaining at the time of landing.

At 1412:26, while the aircraft was descending through 175 feet AGL, its indicated airspeed was 144 knots, with a ground speed of 121 knots, and a rate of descent of 672 fpm. The thrust remained at approximately 64% N1.

At 1412:30, while the aircraft was descending through 153 feet AGL, its indicated airspeed increased to 154 knots whereas the ground speed did not change appreciably, consistent with a performance-increasing wind gust. The PF pulled back the thrust levers, and as a result, over the following 5 seconds, N1 decreased from 64% to approximately 43%, where it remained until touchdown. The airspeed began to decrease.

At 1412:40 (3.6 seconds before touchdown), when the aircraft was at a height of 50 feet AGL, the indicated airspeed was 145 knots, and the ground speed was 112 knots. The rate of descent had increased to 1114 fpm. The enhanced ground proximity warning system (EGPWS) aural alert “fifty” sounded to indicate the aircraft was at 50 feet AGL, which is a standard callout.

One second later (2.6 seconds before touchdown), the EGPWS alert “sink rate” sounded, indicating a high rate of descent. The aircraft’s indicated airspeed was 136 knots, its ground speed was 111 knots, and the rate of descent had remained at about 1100 fpm. The bank angle increased to a 4.7° right bank. The engine thrust was steady at approximately 43% N1.

At 1412:42 (1.6 seconds before touchdown), the aircraft’s indicated airspeed was 136 knots, and its ground speed was 111 knots. The aircraft was slightly below the glide slope, but on the visual segment of the approach and tracking the runway centreline. The rate of descent had increased to 1072 fpm, and the bank angle was 5.9° to the right.

Less than 1 second before touchdown, the aircraft’s indicated airspeed was 134 knots, and its ground speed was 111 knots. The bank angle was 7.1° to the right, and the pitch attitude was 1° nose up. The rate of descent was recorded as 1110 fpm.

At 1412:43.6, the right main landing gear (MLG) contacted the runway. The aircraft was in a 7.5° bank to the right with 1° of nose-up pitch and 3g vertical acceleration, at a rate of descent of approximately 1098 fpm (18.3 fps).

At touchdown, the following occurred: the side-stay that is attached to the right MLG fractured, the landing gear folded into the retracted position, the wing root fractured between the fuselage and the landing gear, and the wing detached from the fuselage, releasing a cloud of jet fuel, which caught fire. The exact sequence of these events is still to be determined by further examination of the fracture surfaces.

The aircraft then began to slide along the runway. The fuselage slid down Runway 23, rolling to the right until it became inverted. A large portion of the tail, including most of the vertical stabilizer and the entire horizontal stabilizer, became detached during the roll.

The aircraft went off the right side of the runway into the snow-covered grass area and came to a rest on Runway 15L, near the intersection with Runway 23, about 75 feet beyond the right edge of Runway 23 (Figure 1). The right wing, including the right MLG, became fully detached from the aircraft and slid approximately 215 feet further along Runway 23.

Once the aircraft came to a stop, an evacuation began. All occupants evacuated the aircraft. At the time of writing this preliminary report, it has been confirmed that 21 of the 80 occupants were injured; 2 of those occupants were reported to have serious injuries.

 

Company landing standard operating procedures

The flight operations manual indicates to initiate the flare between 30 and 20 feet AGL by increasing pitch attitude as needed to slow the descent rate while continuing to reduce thrust to idle. At 20 feet, back pressure on the control column is to be maintained as necessary to hold a constant pitch angle. In addition, the manual states that the pitch attitude at touchdown should be between 3° and 8°, depending on the landing reference speed (VREF) of the aircraft. If the pitch attitude exceeds 11°, there is a risk of a tail strike.5 Also, a hard landing is defined as “[a] landing at a vertical descent rate greater than 600 ft/min when the aircraft's gross weight is less than or equal to MLW [maximum landing weight].

 

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